Tryndamere is .....

. . Basically with a Both have slows, but of course Tryndamere's doesn't actually need aiming Both have gap-closers .... but Tryndamere's is of course faster Both have healing, but Tryndamere can store it until he needs it all the while using his fury for more damage...

So Aatrox is "boring" because it is really hard to stay alive, and his kit is a sub-optimal version of Tryndamere's Tryndamere is "boring" because his kit "synergizes" so well in one particular way, that he is the proverbial one-trick pony.... Although might take offense with this statement.

I do think that once Aatrox get 3,4,5 complete items he might be stronger or more useful to the team in teamfights.