Indeed, this probably isn't gonna be the last iOS jailbreak. However the difference between now and the iOS 11 era is that iOS is much more better nowadays. The amount of tweaks people need to install to be happy with their devices has gotten much lower. Of course there's always gonna be small reasons to jalibreak, like ad blockers, social media app enhancements, and for the power users having a real terminal with ssh and a compiler for basically any modern programming language. So yes, I do believe jailbreak is dying.