All of them sounds like legit answers. The reason why I asked is that I played competitive before and the players are so toxic, that I don't know if I want to keep playing there anymore.
I think how skilled you are depends on your skill, not the game mode you're playing. That said, I don't think quickplay is a good way of determining someone's skill.
Mechanically, no, but you do lack on the game sense that is needed to help you do well in comp that you can't really improve on that much in the other modes.