You are requesting the game to become a single player game?
I find your suggestions strange. I get it that some ppl leech etc. But its up to each individual what they do? There is a kick function so you are able to kick leechers.
Chat can alrdy be turned off? Its a online game and communicating and finding ppl for party is a part of a online game.
Whats wrong with ppl doing higher gr than they cleared solo? Your suggestion would make more ppl feel the need to only play meta builds. Also if there is no leaderboard as you suggest why would it matter? Also dont see why you want to remove LB. If you dont want to compete or see how other ppl are doing then dont open the LB?