The diminishing variety for the mapgen with higher play counts is a known issue. The reason why this occurs is because there is a certain amount of area that is designated to each player as well as a certain amount of pathing between players to ensure maps are "playable" without having things like no paths between teams.
I am slowly working to make it more varied but for smaller maps with more players it is more of a problem as I don't want to have the generator spitting out "unplayable" maps very frequently.
So the soft cap as you called it is known and a function of me being careful to not put out bad maps.
As far as the different size of maps it is definitely a possibility and is on my to-do list. Albeit a little lower on the priorities. There is some different formating for other maps sizes that need to be accounted for. Additionally the generator still assumes square maps so that needs to be adjusted as well.
If you are ever curious how the generator works feel free to reach out to me as well. Always happy to discuss.