D3 wants you to play this game for a long time, not just a few months. I wouldn't expect them to make any drastic changes to the game. Things are pretty well established, with minor tweaking along the way now.
Moving to Suggestions. Link left
Supports aren't a massive failure, they just need better distribution. I have supports that I regularly use, because they help. 4* dilution is an issue, yes, but I must also admit that I'm able to champ them anyway. It's not impossible and I have to take what I can get. I'm acquiring about 20 - 25 x 4* covers per week. That's enough to keep things rolling, despite dilution. But I think your biggest complaint is 5* players taking rewards away from 3* and 4* players. I agree, it doesn't seem fair. But you can also look at it from their point of view, they want the freedom to play SCL 7 and do their clears in 30 min or less. I think rewards in SCL 8 and 9 should be improved so that 4* and 5* players naturally stay out of SCL 7.
Redesign the rewards so that larger rosters don't need (or want) to move down clearance levels.