I agree with you if you are a 1 trick pony, but I think most people can play multiple champions to a relatively competent level that asking what the team needs/is missing is a fair and reasonable way to improve win rate. As an example I'm a D3 jungler that used to main Rengar and Khazix, but can play most junglers fairly well. So currently play mostly Reksai and Elise. Similarly when I get my 2ndary position as top lane I generally ask myself do we need a tank? Do we have enough AP/AD damage? Do we have engage? What about wave clear? Etc. Because it helps guide me between several champions I can pick from. I am not going to for instance pick top lane Riven even though she may be decent now cuz I suck with her, but if we are missing a tank I will definitely take Maokai top instead of something I am more comfortable with e.g. Rengar top because in my experience it overall is more comfortable for the team and leads to more consistent results, while on the Rengar I'd have to be significantly better on it than Maokai to actually make a big enough difference that it would justify picking it for me.