"Diamond is still a progression rank for most players"
I'm gonna have to go ahead and disagree with you on this one. The bloated diamond ranks we get by the end of the last few seasons is the developer's pat on the back for showing up, and has almost no bearing on ability. Most of those players should be in platinum, not upwardly mobile. But Respawn has found value in allowing mediocre players to think they're better than they are. Go figure.
"A better solution is to adjust matchmaking by filling solo players into the rank below"
I would have said "the tier below," meaning if you're high diamond then, sure, okay, have a low diamond match with your randoms. But putting a high diamond player into a platinum lobby just because he solo queues? I'm not feeling good about that. Though maybe I'm too uptight about these things. You tell me.
"This would smooth the skill gap from Silver to Diamond, reduce sweaty lobbies, keep queue times fast, and preserve highly competitive team play."
Wow, that's a pretty heavy lift for one small, and possibly questionable, change to the method for matching high-rank solo queue players. Not sure I'm able to do the math on how matching a solo diamond player into a platinum lobby is a sweat-reducer, speeds up queue times, or preserves competition. I see how it could look that way at a glance, but I doubt that it would have any material effect on the "problems" that solo queue diamond players complain about, and I can promise you that platinum players wouldn't love it. Though not sure how their lot could get much worse.
vVv_Bjoergen_vVv
"This still won't change the fact that most masters, after reaching a rank, will move with their friends to Pubs/Wildcard and ruin the game for others there."
Or move to a secondary and start their rank grind again, or maybe do a couple of rookie-to-whatever runs for fun.