Non-Uber legendaries are fine, but limit one per team of six. I mean, who's going to argue that Suicune and Registeel can't be defeated? Registeel doesn't even qualify for OU competitions. Psuedo-legendaries all have a 4x weakness, except Metagross who has to deal with Earthquake and fire attacks. Garchomp may be Uber, but it still is decimated by Ice Shard and Ice Beam, which have plenty of users at this point.
To me, if you can't pick a team without using more than one Legendary, then it portrays you your strength as a player. Same with overused; two overused Pokemon, and the rest should be underused while capitalizing on their strengths, not exaggerating their weaknesses.