The photos are neither low-quality nor highly-compressed. I personally can't tell much of a difference 95% of the time and I'm a technical person. Here´s a comparison and a closeup, left image is the original, right one compressed with the Unlimited Storage setting:
The first picture has a very noticeable color shift (left is warmer, right is colder) - I am looking at it on a professional 10-bit 4k display which might be a factor, but I would run away from any storage that would cause that :-O Detail looks horrible on both, difficult to say which one is worse and how well do they match. On better photos that would probably be noticeable (my color vision is 100%).
I'm looking at it on a Dell U2715H, which is not a professional display, just a consumer one with above-average color quality and good calibration out-of-the-box, and I could spot the temperature shift immediately as well. Also, as you say, the details are bad.
I'm wary of services that auto-compress images, because a) I want my bits to stay the way they were originally captured, and b) every now and then I have to print a photo I make, and then suddenly all those details matter for the print quality.
