Matching UI to designs was horrible on Android, at least as of ~1.5yrs ago. Even if designers were shooting for "Material". Plenty of rough edges. I wouldn't say 2x-3x longer for a typical project, though.
I could see there being issues with relatively new-to-Android developers not appreciating the degree to which advice from the official docs, especially relating to structuring applications, should be taken with a largish dose of salt, leading to slow-and-getting-slower development as an Android project went along.
To get to the level of world class competitiveness i'd say it's true. if you want to compete with say instagram then android is such a PITA to design for.
As for your second point, i've always followed the official docs,are you saying there's another way?
Square's guides and libraries in particular were a great place to start when last I worked on Android (2017). They filled in a lot of dumb gaps in basic, common functionality, and their guides and blog posts on Android topics generally left me feeling more confident in them than in Google's Android team. They were among the ones calling "the Emperor has no clothes!" over fragments, for instance, and they described and built alternatives.
It does look like they've abandoned a couple of their big view-related Java libs, which makes me wonder what they're using now. Seems they've switched to Kotlin for a lot of stuff.
Don't remember their blog being on Medium (ick) but it is now, looks like:
I could see there being issues with relatively new-to-Android developers not appreciating the degree to which advice from the official docs, especially relating to structuring applications, should be taken with a largish dose of salt, leading to slow-and-getting-slower development as an Android project went along.