We are sort of talking about two different things. I don't disagree with you about anything you just said, Sam is clearly the worst dps for all the reasons you just mentioned. I definitely agree that they should continue working on balance, improving balance will help improve their chances of getting a decent static, but this is not the main reason why pug parties lock sam's out. Say you buffed sam or blm damage up to the point where they were doing so much more damage that it was even meta for speed runners. They would STILL be locked out of pugs and many statics solely because everyone else in the group would have worse parses. If they did so much damage that it was clear to everyone that they should have a sam, it would just replace one issue with another, they would replace drg and with that brd.

So yes absolutely improve balance, but without utility and especially dps buffs there will always be a large amount of resistance to others letting them into groups.