That's been my experience, as well. iTunes has become my go-to service for rentals. One of its benefits is that the quality is consistent, not variable. Unlike Netflix, which usually takes a couple of seconds to ramp up to full quality, iTunes either plays properly or buffers until the bandwidth...
Canadian Netflix offers 3 different plans. Basic is SD, Standard is 1080p and Premium is 4K. I have the standard plan and the 1080 quality is excellent - I have to look very closely to tell the difference between blu-ray.