Please note:
Infallible doesn't mean "never loses"
Infallible means "doesn't make mistakes".
As any halfway-decent chess player knows, it's possible to do everything correctly, and still lose.
I think what's really irritating Panther fans (well, irritating me, anyway) is that T'Coates lacks any real agency. He's always reacting to events and being led around by the nose. And even when he DOES know what's going on, his plans all seem to boil down to "I can't do this by myself, so I should get help from someone else." (often, but not exclusively, African-American superheroes)
Contrast that with RJ's KiB one-shot, where T'Challa is confronted by a new foe, considers his options & resources, and comes up with a plan to save Wakanda that doesn't rely on help from Americans or an army of
manes ex machina.