You could argue that Gmail’s new UI is slow. That’s fine and correct. Arguing that they should maintain an outdated view forever seems to forget that that’s not how any of the web works. It’s already weird that the view survived past 2009
Google kills whole successful products, what made you think that they would support alternative UIs used by dozens of us?
Arguing that they should maintain multiple views is just ignorant of the world we live in. You will be disappointed further.
Whether or not a trillion-dollar company with 170 000 employees can afford to maintain two views for a product with 2 billion MAU or make it not suck, now that is really irrelevant.
that remains to be seen
It’s how Google’s business works, maybe, but that wasn’t the argument.
Imagine an organization which wants to buy Google's package for organization. Perhaps some government body. And that body has a regulation that requires certain accessibility features from services provided by contractors. So, even if very few, or even if nobody in that government body needs good accessibility, the IT will not buy a service from Google because one day someone will come and sue them for buying stuff they shouldn't have.
So, it doesn't matter what fraction of users actually needs the "basic HTML" view. The new one sucks from usability perspective, and especially from accessibility perspective. If they cancel the better version they have... well, I'd be all for suing the government agency that decided to use GMail.