In my experience, it's a certain kind of person that brings up the issue of the opposite sex being rubbish in bed. It's usually women to be fair I think most men are just happy that they are getting something.
But when I think about the girls I know that have a big bee in their bonnet about how "most men are clueless/selfish" in bed, they are also girls that are quite stuck up about other things in life and like to complain and also talk down about others. I think the problem comes in attitude tbh. I think if you are turning sex in to a kind of competition where you are judging whether your partner is good or bad you are missing the point. Everyone is turned on by different things and I think it's easy to have fun in bed if you just ask the right questions, eg ask each other what turns you on, then talk about what stuff you've done in the past and get ideas from that eg if one of you has done something that the other hasn't, see if they want to try it, and then ask so what stuff haven't you done in the past that you've fantasised about, and see if you want to try that. Obviously you have to respect that your partner might not be in to something particular and that isn't right or wrong. So I wouldn't judge somebody for what they are in to.
Not every sexual partner you have is going to be ideally compatible and that's part of life but I think if you are the type of person that is continually disappointed by your experiences in bed and blaming other people then the problem might be your own attitude?