Yeah. There's a series of problems with the ranking system, and this is one of the more pressing ones.
Personally, I think you should be able to lose tiers, not just ranks. And it should take more stars and more ranks to reach the next tier (5 stars and 5 ranks per tier, except for 5 stars and 3 ranks to reach Bronze from unranked), and switching streak bonuses from an extra star to extra XP/marks. You can't control the quality of players on your team, but you *will* see upward momentum over tens or hundreds of games if you are actually skilled. There's people with 1000+ wins in the top 5-10 in pretty much every DC, which directly proves that if you work hard enough and are actually skilled, you can get there no matter how badly you get screwed with teammates. But the smarter thing is to only play when the high skill players are also playing - usually prime time, especially on weekends. I've noticed a dramatic shift in overall quality of games and teammates when I play during those times, versus early morning hours or noon or something like that. If I was focused on trying to push rank, as opposed to just playing to have fun, I would probably only play when there's a high density of high skill players active.
I don't think there's anything that can be done about people trolling in Crystal with "off spec" classes. Being able to de-rank to Diamond wouldn't fix anything. The only fix for that would be class-specific rankings, but people tend to freak out when they think about having to do a rank grind for each individual class they would like to play, even if you started like two or three tiers below your highest tier (so if you have a Crystal, your other classes would start at Gold 5/0.)
What I think folks don't realize or want to accept is that if you want actual skill-based matchmaking, you're going to have to create an actual, significant grind to move through ranks. Like, where it would take hundreds of games on average to make it to Crystal instead of potentially just like 50 or 60. With how easy it is to rank up right now, rank really means absolutely nothing about player skill, not even within Crystal. I've personally seen multiple top 30 players play like complete ass (maybe they were playing "off spec" though) and low Diamond players playing out of their minds.