I think the only one of those he has that he [i]knows[/i] about is the first one.

And, well... his ego alone is an enormous nerf. What he [i]could[/i] do is a far cry from how much effort he actually puts in and it keeps making him lose. Fate route? Leaves Saber alive after overpowering her, she ends up getting Avalon; UBW he doesn't even bother with the armour and passes up an opportunity to kill the main characters because some ash got on his clothes (and he loses the fight with Shirou because, aside from not bothering with armour, he doesn't take it seriously from the start and UBW is a natural counter to bladespam), and in Heaven's Feel... once again, leaves something for dead after shooting it a few times and wanders off. Gets consumed from behind. Hell, he only won his last fight in /Zero: first one ended when he was told to leave (though he was just going for the same but more), second he lost a dogfight because he's not actually that skilled, and the third he actually won.

It takes pretty much an army of heroes or having something like Excalibur to make him do things even slightly properly. Even then he still holds back (plus using Ea at full strength is a bit stupid: it's not like he has another planet to go to).

And the way most nerfs would work out is that he'd have no ability to be doing things that he wouldn't be doing anyway? It'd be a bit invisible. xD