As much as I sympathise with developers over headaches caused by themeing, I believe users (myself included) would be less up-in-arms about it if applications were less ugly by default. And boy howdy is libadwaita ugly as sin.
I’d be perfectly willing to tolerate a mismatched system, if the individual components looked at least okay. Like I’m not going to get e.g. steam or discord to match an e.g. Windows 9x theme, and I’m mostly okay with that because they aren’t horrible to look at. But, say, File Roller? Absolutely not. Horribly ugly.
C++ is pretty alright, IMO, but the syntax is kinda clunky though, I think probably because of some historical baggage.