Thanks for the kind feedback! The difficulty curve is definitely the thing that I fiddled the most with, but I wanted the mass of 100 to be very hard to obtain, "equilibrium" at 70-80 is actually where I aimed at initially (actually at 80-90, so maybe it's slightly harder than I wanted it to be). The reason is that this point in the game it becomes hard to push the amount gradually, but it's still possible to make a "pendulum" of sorts: give up some mass strategically to get more complex shape, and then use this shape's big perimeter to overpower enemies and push past this 80 mark towards 90, I didn't want to give up this emerging change of strategy. 
But it's true that in the end it also created a frustration point of just getting to 80 pretty fast and endlessly hovering there, too much of a shift. I do plan to keep updating the game and address the difficulty by introducing a couple of different "levels", just 3 to 5 total, each available after getting to a 100 in the previous one, and then back to square 1 (literally) on the new level that slightly adjusts the difficulty curve and changes enemies to a different kind just to spice things up. For example I really want to have a level with enemies that shoot lasers that cut through the whole mass in a line, I feel like this would make the emergent shape even wilder. And I hope as a result I can make the feel of each level more consistent, and the difficulty curve into something varied rather that the current "easy for 5 minutes, then always hard".
I can't promise anything, but I really want to make this game into something more complete, so hopefully you can check it out later!