I have too many thoughts on this that I've been struggling to answer. I think a simple answer is "I half agree"? But there's more to it than that.

Objectively speaking, Taki simply got less focus compared to some of the other characters. And by focus I don't mean simply being on screen, but being the central character of the scene/episode.

However I don't think that paints the full picture. Raana got less focus as well, but people seem to be mostly satisfied with her as a character. I think it's because the focus she got was enough to fulfill the role that they gave her. You might argue that it means she's a shallower character, but I think of it more like they gave her enough depth as her role in the story demanded. They didn't promise too much and they delivered enough, so she feels like a balanced character.

With Taki on the other hand, I feel the balance is disrupted and that's why it stands out more to people.
They set up a lot of things with her, so from a certain perspective her characterization or shaping is actually quite detailed. She has her inferiority complex towards her sister, which further developed to include Sakiko. She's always putting pressure on herself which then overflows to affect those around her. She struggles to to be honest with herself and express her feelings properly. She once felt she's not qualified to live normally. She felt that Tomori's words saved her and they always resonate strongly with her. Yet she struggles to connect with Tomori and doesn't allow herself to show her vulnerability in front of her. She's still thinking about Crychic but tries to tell herself otherwise,.. I can go on.

But contrast to how rich her character background is, how much of it is put under the spotlight is really lacking. The anime didn't actually get to the stage where most of those things are delved into and explored in more detail. And Taki's issues that are set up aren't properly dealt with (yet).
So there's a sense of unbalance between the depth of the character and the focus it was given.

Episode 6 which is her focus episode doesn't actually solve any of her problems. It really only gave her a temporary (physical and metaphorical) bandaid and she simply kept going. And in the rest of the anime she gets a few scene to showcase her growth, like apologizing to Tomori for bringing Umiri, praising Anon for not giving up practice, and sharing the guilt with Soyo for using her as well. It shows how she reflects on her actions throughout the story and tries to learn from them. But a lot of the core issues and themes surrounding her are still left unexplored. I think that's why many people are left with the sensation of wanting more, because there's a lot more unexplored potential in there. That's why many Taki fans are hoping she gets a proper arc in Animuji.

There's also the fact that a lot of Taki's characteristics and "charm points" are shown in the background or portrayed through actions rather than said out loud, so it's easier for more people to miss it (not many people would pay attention to the score sheets that Taki makes for example). Plus she doesn't have many "highlight scenes" for people to point at. So some people might be left with the impression that she's lacking as a character more than she actually is, because they missed a lot of the details. But I would classify this (at the risk of sounding condescending) as a "casuals" problem.

Another aspect to this is how much she as a person clashes with those around her. Compared to Raana who has too little friction with anyone, Taki can be really harsh and strict, and the role of putting pressure on others is often given to her. This makes her "stick out" more, and people watching the show might feel like her actions are lacking in justification because the time she was given to make the audience empathize with her is limited. (As I mentioned, the show does give you enough information to work it out yourself but not many people are prepared to do their homework.)
But I don't think she was given that role with malicious intent. In fact, Yunico-sensei tweeted about this when episode 6 was airing.

"It's easier to live a life without conflicting with others. But for the sake of ideals and goals, one must be prepared to face conflicts, to speak up boldly even if it means being disliked. Some things would never progress if there were no such people.
I admire people who are willing to take on such a (commonly seen as) undesirable role. However, since it's a sort of self-sacrifice, it would be great if they could reach out to someone to vent their frustations and cry it all out, before it hurts so much that it completely crushes them. Revealing your vulnerabilities to others is not an easy thing to do though."
[source: https://twitter.com/ForrevaEiEn/status/1684466188137693184?s=19]

This quote shows that the writers are aware of what the impact of such role can have on her reception as a character, and I don't think they did it without being prepared for the consequences.
That second part in particular actually gives me a lot of hope that they properly thought about her future shaping and development as a character. Taki is still bottling up her struggles and frustrations. That outcry and the readiness to show her vulnerability are not things we've seen yet.
Of course this most likely means that she'll face some painful experiences going forward, but that's honestly a given with how heavy some of the stuff they set up for her is.

I think next season, Taki will be given more focus and some of that set up will finally have a payoff. I'm not saying that all of her problems will be solved in the anime but at least some of them will. I know some people say there's no room for it next season but I don't agree.

First of all, they confirmed in multiple interviews that Mygo's story will continue even next season. The focus will be more on Avemuji but it's still the story of 10 people. And in Mygo, Taki will be the only one left who hasn't gotten her arc yet (Raana has the movie, so that is sorted out).
Taki's two keywords in her character introduction were "inferiority" and "future". The keywords basically sum up the character before and after their development arc, and Taki is the only one left where we haven't seen that "future" and what it means to her.

Second of all, Coco alluded to Taki and Saki having their reunion and the clash that could result from it. I think it's on purpose that Taki is the only crychic member who's yet to meet Sakiko again in the anime. And it also feels like there's a general ban on Taki sharing too much about how she feels about Crychic (like during the rain event).

I think that based on Coco and Yunico's quotes above, it might go something like this:
Taki and Saki will meet again and clash. It causes Taki's sense of inferiority to go in overdrive and her complicated feelings about Saki and Crychic in general will make her mental state spiral downwards and make her feel lost. Tomori who said that she won't let her feel lost alone (in Breathing Next to You event) will certainly reach out to her. Taki will finally be able to vent her frustations and cry it all out. And by showing her vulnerabilities to Tomori the two will become closer together and Taki is able to get back on her feet.

Of course she might also have other stuff to deal with besides her main arc, like leading the band or taking part in someone else's arc (like Umiri's).
Taki is former band mate with two of the Avemuji members and classmates with another two, so she will have many opportunities for potential interactions.

Of course this is just a guess, there are still too many things we don't know yet.
But basically I think that Taki's complexity towards Saki and Taki's struggle to connect with Tomori are two aspects that can be dealt with in the next season. While plotlines like Maki and solving the sense of inferiority for good.. are things that will be dealt with in the game long-term.

And lastly, Mygo already laid down the groundwork for the setting and basic character introductions and so on, so Avemuji doesn't have to go through all that again. That basically means it should have more breathing room in terms of how many things it can focus on.

I'm optimistic so let's wait and see.

In short, I feel like they gave us enough clues to learn what kind of person Taki is, her pains, struggles and ambitions... But I still want to see these aspects of her given the attention they deserve. Taki is clearly still suffering and it would be sad if she had to endure that in silence again without getting the relief she needs. So I'm looking forward to next year.