It's not a good idea to take Miguel's criticism of .NET seriously in the last couple of years, after the falling out. Give it more years and we might just hear the similar style of statements towards Swift and Apple's ecosystem now that he is promoting it.

The only thing it does is spreading the FUD further.

(I knew it was him even before opening the link, as he's the only source of vocal publicity of this kind)

I don’t know what happened but these days Miguel does seem very salty about w/e happened at his time at MS. Like you, I would take what he says with a grain of salt.

Basically after Xamarin got acquired, Xamarin.Forms got rewritten into MAUI, Mono Develop was killed in name of VSCode (after existing for a while as VS4Mac) with no comparable tooling, Mono only exists as runtime for iDevices/Android/Blazor, Mono linker got repurposed as Native AOT trimming, most of the Mono BCL was merged with .NET Core efforts.

And that was it, regarding Xamarin story in the .NET ecosystem.

I assume, like with any acquisition, what they were promised and how things went down, wasn't quite the same.

His enthusiasm for SwiftUI in particular is a bit hard to reconcile with my experience using it. It's nice on the happy path but you very easily stray into areas with baffling compiler errors and terrible UI performance.