Thyra wins because Kiryu doesn't hit women :)

Jokes aside though, Y1-Y7 era Kiryu should be stronger than do5 era Thyra, but that's because I did actually use Kiryu to describe Thyra's in-lore combat prowess to Parr a while back, and modeled do5 Thyra specifically to Yakuza 0 era Kiryu, while ChinaLT version of Thyra should be more like Yakuza 5 era Kiryu. So in the sense that I directly modeled her, if we compare them at similar experience level brackets, then it's a close call.