I think the issue is a lack of informed consent. Some of the commenters seem to think this isn't a "big deal", since the changes were relatively minor and made to benefit the user.
Let's draw from the real world: even if you have zero STDs, and use a condom, it is a serious crime to have sex with someone while they're asleep - because they couldn't give consent.
It deeply troubles me that I keep seeing this mentality that there must be "harm" for something like this to be a problem.
I saw similar logic used in the article on Google using "anonymized" credit card data - that people's feelings about the matter are invalid, since there's no harm if the data is anonymized.
Frankly, the word that comes to mind when I read these articles is not arrogance - it's entitlement. Google feels entitled to do as it pleases, because it feeds it knows better than you.
I'm almost wondering if we could do some sort of crowd auditing of play services changes, automatically grab changes pushed via play store, pass through appropriate decompilers and disassemblers and highlight modified sections, similar to what tools like bindiff do... I know, I know, install MicroG/switch to an iPhone/burn your phone with fire, but many people run these devices and would be interested in any impacts like this being had on user security and privacy I'm sure.
Google is fucking creepy and it probably shouldn't be legal for them to bully me into using Play Services.