I never argued that Google helped XMPP, I'm arguing that it isn't applicable to the "extend, embrace, extinguish" crap that people keep parroting like it's an actual playbook used by tech companies and not just some silly nonsense created by some middle manager at Microsoft 30 years ago lol. The users Google brought they took, at worst it was net neutral.
like making it hard for their servers to be interoperable with others
Because they forked their own deviations of XMPP to work with the updates made to Google Talk. It's original state was left untouched and by no means "extinguished". This is just another example of corporate freeware winning over open sourced because of a more polished product.
their slow adoption of new features
I assume you mean Jingle which they adopted in 2007? Why would slow adoption of XMPP features into Google Talk affect non Google Talk XMPP users? They were always free to use XMPP without Google Talk, just as we're free to stay on Lemmy/kbin/Mastadon without Threads.