I don't think I've ever seen a tank Yi like we've seen a tank Yasuo. Yi builds LS yes but at most his defenses would be from TF for the health, tabi's for some armor, Maw or Mercurial for some MR but that's it. Aatrox has to build tanky b/c he has no natural defenses in his Kit outside of his LS every third hit which is not consistent without a truck load of AS or his passive which makes him a good initiator but a poor assasin.
Comparing Yi and Aatrox is a grasping metaphor that doesn't really resonate. Yi has true damage, sustain and high mobility that allows him to go in and assassinate a high priority target or 5 and then take two towers. Aatrox can duel 1v1 but has poor team fight presence. His Dark Flight is interrupted easily, his slow is easy to avoid and he's not that hard to kite.
If you ask me Yi fills too many roles in his kit. Burst, sustained and true damge, sustain, AA resets, no targeting abilities and high mobility and slow immunity. The only thing that saves him from true OP status is that he's got a bad early game and if he get's starved from kills then he's useless. Those are big if's in my opinion.
Aatrox is not even comparable nor Xin. Neither of them do the amount of thing's Yi can do.