Regardless of how Cloud started out, he still beat Sephiroth, and Sephiroth is insanely powerful. His "sickness" was due genetic/mako infusion experimentation, which made him a bit like Sephiroth, and a lot of the stuff he did was while under the influence of Sephiroth's telepathic powers, because Sephiroth fused with Jenova and Cloud was experimented on with Jenova cells. The experimentation screwed a bunch of his memory up, and he was also virtually superpowered thanks to mako energy and Jenova cells.
So,
A) Genetic experimentation wipes you out when you aren't a First Class Soldier
B) Didn't remember who he or Zack was
C) Never even knew who Aeris was before he met her, even without the amnesia
D) I don't seem to recall him beating the hell out of Aeris, I recall Sephiroth telepathically trying to make Cloud kill her, which he was stopped from doing
E) Was recovering from being mind raped when Sephiroth fell from the ceiling to kill Aeris, which he did instantaneously, not exactly much time to intervene
F) I wouldn't want to tell them he was dead either, even if I remembered.
I'm not saying Cloud isn't kind of lame. He's just not lame for those reasons. And certainly not lame for being bad at fighting.
