I think Demi asked us all this question before iirc, but I don't mind answering again.

Elio and his siblings were (A) students, who got excellent grades in every subject they studied. It's part of the self-imposed perfectionist mentality that plagued them to not only uphold the family name but not embarass their grandfather, Wolfgang.

Though all of them were studious, Elio and Ardyn during their respective days in T.U.A. (Tork-Unovan Academia) were the ones that went above-and-beyond - getting constant strings of A+ grades and receiving high honors in general due to them being the eldest of their respective sibling groups, thus seen as the "face" of the Argentiums at the time - adding even more pressure for them to succeed, which they both handled with the grace of a Swanna, an Alolan!Ninetales, and a Milotic respectively.