Speaking of async coroutines, my belief is that they don't get used enough in other game engines because their lifetimes are not tied to anything - you have this danger where they can outlive their entities and crash your game.
Async coroutines in the way you are describing have terrible/unpredictable cache/memory access behaviour which leads to bad performance. Every time you switch coroutines you need load memory from (most likely) an unrelated region causing slowdowns.
Yes, I do get this. I made choices to prioritise an abstraction that, in my opinion, makes you more productive. It's not going to work for certain kinds of people or games.
One of my original motivations for creating Easel came from my experience playing (and making) webgames, which in general are coded in JavaScript (or TypeScript). I love webgames as a method of delivering multiplayer because the biggest problem is getting players, and I think the low-friction zero-download really helps with that. So this is the world I am trying to target. When I remade my old webgame in Easel, I found it to be many times more performant and am now able to target much lower spec devices. Not to mention, determinism is a non-issue now.
I get that some people are going to love Easel and some are going to hate it, and that's okay.