I never found the mobile apps to be slow (they're "semi-native", made in Xamarin, in the same way React Native is "semi-native"). The Android integration is not great (it misses password fields sometimes) but this is because of the platform itself, not the current app architecture.
The Electron app (for desktop) and browser extensions are indeed slower than they could be, and native mobile apps won't fix that.
Agreed. The good news is this is changing, they have native apps already in beta: https://bitwarden.com/blog/native-mobile-apps/
I'm using the Android beta and can confirm it's much faster.