Have you personally noticed any downgrade in your experience yet? Each year I waffle back-and-forth about whether the OneMedical membership fee is worth it, but only because I'm pretty healthy and don't get to use it much. Whenever I do, it works great: book an in-person doctor's appointment same-day/next-day in 10 minutes, get seen within 5 minutes of walking in, no need to fill out an in-take form with my complete medical history for the umpteenth time, and prescriptions and follow-up all handled seamlessly on the website.
The Amazon acquisition seemed like the best outcome we could hope for. Experience says it's unrealistic for OneMedical to remain independent forever, and Amazon has much better customer service than almost any other big company with a broad customer base. Insofar as the OneMedical experience was stellar mostly because it was being subsidized with ~$1B in VC/PE money (which is plausible to me), belt tightening was inevitable.