Go-Through platforms would still have to remain active objects anyway :-/
I'm afraid I can't make platforms background due to the interactions with them, and their layering.
I'll try a little more but that might lead to a dead end.
Also, I kind'a proved it's the events and actions (=project's complexity) with those 2 videos and nothing graphics-related.
I will continue to optimize the code, and the 30fps version for stress test failure turned up to be a good idea, as it makes the game playable on most devices that can't handle the stress test.