I really haven't had any real issues with Prime shipping. I think I've had like 2 things in the past year or so that arrived in 3 days. Twice, I did have an incorrect item arrive so I had to do a "return". But they sent out the correct item(s) and I got them the next day.
I will say that there's an Amazon distribution center about 10 minutes from me. So I actually see a decent amount of next day delivery items; that I assume is due to being so close to one.
And sometimes, I'll choose the later delivery date if I get a digital credit with it. I like to save those up then use them to get a free movie.
Finally...if Amazon isn't keeping their end of the "Prime 2-day shipping" deal, then cancel. Nobody forced anybody to pay for it. And if you do cancel it, you'll still have whatever time is left on it to use for free shipping.