1.) There are more problems in the match making than just role stacking though I wouldn't mind them testing this a bit better since a full dps team winning seems to be the outlier result in such matches.
2.) The NIN LB is in fact a bit too much, but they don't seem to understand what about it needs adjusting. SAM isn't really an issue in CC because at most you only have to deal with one at a time and you can see their limit gauge. You can even make it bigger and reposition it if you aren't noticing when it's full. MCH LB is only ever a one shot if you play sloppy or people dedicate damage to you. Chainsaw is so rare it's kind of a meme to say it's a problem.
3.) Potions represent a fun and depending on the lobby important part of gameplay.
4.) Personally, I don't get why they don't just spawn the rewards in your inventory upon the first log in post season.