And here we have another intrusion of Google into our home. It's clear Google has no respect for anyone's privacy and is now a part of the problem.
Yes they collect a lot of data, but 1) that's exactly what allows them to provide the services that their users want, 2) they are very transparent about it (see My Activity), and 3) they seem to take security more seriously than the competition.
I do my best to support the companies that respect privacy, and I make sure my own startup's products give our customers the privacy that I would want for myself.
I wish there was a certification or something, sort of like b-corp, that could indicate that a product doesn't gather any personal data (as opposed to just being GDPR-compliant, which allows collection but imposes various processing/deletion requirements).
EcoBee is a great HomeKit-aware thermostat and you don't need to sign up to their account to use it (although it'll keep nagging you to, it's not required).