I think Catalyst is basically positioned as a stopgap for iOS developers to get something running on macOS, you can optimise it from there and later split out some code for a specific macOS target.
Yes, and this was my experience with the JIRA Catalyst app too. It's harder to implement new features in native apps, and it's a lower priority (on desktop) because it only affects one platform. So the project is deprioritized and never gets any updates.
The iPad version of Teams is so much better than the Electron version. If you're a member of Teams across multiple organisations or, god forbid, multiple accounts, the Electron version is basically useless. You only get notifications from the org you're actively using, and you can't switch accounts without completely signing out of one and into the other.
The iPad version just lists all accounts and all orgs in the sidebar, no trouble.
It's both rather mature and completely immature to my understanding. There's a C#-based React Native codebase that's been mature for a while but practically no one uses today unless they have to. There's a brand spanking new, mostly finished C++/WinRT codebase that Microsoft took on building themselves (from scratch). It still has the Beta tag on it the last I checked, many C#-era plugins need extensive rewrites to support it, and it doesn't look like Facebook and the React Native core teams entirely trust it just yet for production development. (On the other hand, it looks like the implication is that the Office team has been dogfooding it from day one, it's roadmap is driven by whatever the Office team needs to ship to production today, and if there is a confidence bar for Microsoft dev tools "the Office team depends on it" has always been an interesting maturity bar.)
It's fast, much faster than the web version. But otherwise pretty bad. I kept being frustrated with it too much and switched back to web.
And Catalyst is supposed to be "more native" than iOS apps running on macOS directly...