Hi 
Ashley, just recently subbed to C3 and found I'm having the jank issue as well. I appreciate everything that's gone into providing a great engine and have read enough around the forum and the Chromium bug reports to see that you're trying hard to get a result.
To be honest though, I understand the frustration people have been having around this. I also appreciate you taking the time to respond here.
Elsewhere you mention that competing game engines are having trouble as well, but I've recently found this not to be true. I've replicated a simple test similar to OPs identically in C3 (using all possible combinations of project settings), Clickteam Fusion 2.5 and Unity and found no issues on Unity and only minor stutters on CF2.5 - tested on Pixel 4a5G.
I'd love to use C3 for my project as it does indeed leave CF2.5 (and Unity as far as ease-of-use is concerned) in the dust when it comes to performance. However there's this issue of jank, caused by a complex third-party system that the C3 Android build depends on.
You've also mentioned that you're not considering the option to build an APK without the WebView/Cordova wrapper process. I'm sure you have your reasons for not going native, but is there no question of investigating an alternative Android implementation that doesn't have the jank issue?
I've upvoted this Chromium bug report page and will be submitting a separate complete bug report.
This is a deal-breaker for me, I'm not sure I can be satisfied a project that will be janky on some devices, not others. Regrettably I'll be cancelling my C3 sub if this can't be resolved.