I agree completely, the Amazon app was great until they decided to “upgrade” it around November. It does work a bit better on the newest Roku models (Ultra) as its more responsive but still, they made it overly complicated and losing the ability to scrub frame by frame is a HUGE loss…
I have had PRIME for years for the 2 day shipping anyway (and I really enjoy a few of the PRIME originals) so I will put up with it, but I use it a lot less than I did when the channel was simple (but functional).