I don't actually think that (a) is nefarious; I'm pretty sure any of the companies that I listed will personalize any server responses based on the user. If logging interactions with the product and personalizing based on that is an ethical concern at that level then I don't think you'll be able to justify working at any major web/app companies in general. I had a Bloomberg interview where the systems design question was to implement exactly "user logging for contextual personalization in other places".

I think most users genuinely do prefer to get personalized suggestions instead of irrelevant ones. Firefox is still doing this by default implies pretty strongly to me that the feature is a meaningful benefit to the product, and isn't just in Chrome as a covert data collection mechanism.

I don't believe that (b) is true for Google (paid placement in autocomplete). Google, for all it's flaws, does consistently mark Ads as Ads. I'm pretty sure smaller companies like Yelp and Uber are much more likely to be doing some "secretly paid placement" than Google (but I'd still presume any one of them is not).