I think C3 needs to redo that "System update needed" page. 40% is to large, i bet some cheap no-name phones with android 5/6 are still being sold.
I checked my old android phone and SystemWebView is under optional updates - so major % users - i could bet almost all don't update it.
If you take it from app sell/adds perspective, some points:
* major clickers are kids. I bet alot of them use old parents phones(cheap ones), so 40% could easily grow 80%+. Some might update webview so you could subtract ~ few %.
* Alot of expensive ones(top end) are bought by people that most likely will not click/play games. Its overall % phones sold. That push unusables % even higher.
* Problems with Having Current error page: it is to confusing, + its in english, its to long and kids can't read it(in some counthries even older users can't read it). Good fix would be -> System update needed > Line 2 Update system webview and link to android app store. My cousin that's 8 year old, already knows what update means and if there is link, he most likely would click and do it, even if he can't read the rest.
*It takes few years! for % to go as low 20% what would be good enough. Or even longer, as it takes years before batteries die for phones from 2013-2016.
To OP, just use c2runtime for apps that are simple. If you already developing large game, then just set min android to 7.
You should also consider who you target with app and then choose runtime you need.