I know what you mean but the best players usually pick the best chars, if we nerfed kk blood god just because mr aquaman does well with him, it would be mistaking his skill for KKs power
A moot point, a skilled player will never make a mid/low tier character look high/top. He will make the character look viable for tournament play, but nothing else. If the character doesn't have the tools or right design, it's impossible for it to be perceived as top; a player with great footsies, yomi and defense will only show solid gameplay from mid/low tier characters.
A perfect example comes to mind: DJT's Fisticuff Johnny Cage. He makes the character look good, but never overly powerful. Now, I'm well aware NRS decided Fisticuff need to be adjusted shortly after DJT showed what the variation could do. Having said that, look at Erron Black: it has been nerfed several times now and the character still has better tools in comparison to many others in the roster.