When they rose the price of Prime from £49 to £79 and bundled in Prime Video I wasn't all that happy and until Grand Tour was released I had yet in the years since that increase to find a program I wanted to watch on there. I'd check, see if it was on Amazon or Netflix before often purchasing it on Google Play.
But 90% of the time that a show is actually on there it's not included. I wanted to watch Stargate SG1 the other day and they're charging £2.50 per episode, no offer to buy by the season (and the US price is listed as $1.99 but I bet that doesn't include VAT)
A separate site of what's available as part of the subscription would be good, tying it in with Amazon's full site doesn't help.