Another good reason to run your own private DNS resolver is censorship. I originally set it up after my ISP was sued to block access to thepiratebay.com. The court was satisfied that a DNS blackhole was good enough..
Disclaimer: I work for Google.
We need to normalize people using Pi’s for at-home DNS just like we did HTTPS.
Can you explain why giving a complete list of URLs you visit to the worlds largest advertising and data gathering company isn't dodgy? If you can't see why, then you appear to have drunk the SV Koolaid.
tldr; If millions of people do a silly thing, it is still a silly thing.
But it depends what/who you trust. Say you're based in the US work for Google and want to whistle-blow about some nefarious defense/Pentagon contracts, then staying away from Google (or US based Tech firm) infra as much as possible would be sound advice.
Even if you're just a consumer you should be interested in degoogling your life including not just google DNS but their stupid web-fonts and google auth API's. Google is still going to get lot of your traffic no matter what you do but every data point you can remove is good - even if it adds zero to your bottom line at least you will maintain awareness of how you get milked every day.
Your router doesn't need to support it, one of the complaints from business/school admins or even just people trying to run pihole network wide is that DoH bypasses network level DNS setup
The ISP will do the least legally possible it can to satisfy whatever these external players are coercing them to do. The recording industry does not pay your ISP. On the contrary - they sue them to court and try to force them to implement solutions to censor your internet without any compensation. All these solutions cost the ISP, so if the court is happy that removing the DNS records from the ISP's primary DNS is sufficient, then so be it. The ISP has no incentive to be hostile towards you or implement any more blocks than the absolute minimum they are legally required.