It used to be that in my area (NC Triangle), most items on Prime were available with 2-day shipping, and often same-day or overnight.
As of the last month or so, the minimum time seems to be 5 days, with a large number of items in the 10-15 day range.
I'm no Amazon lover; I view them much the same way I did Walmart 10-15 years ago. They've recently had a lot of quality issues and the prices aren't as compelling as they used to be. If they can't even offer fast shipping anymore, I can't think of a compelling reason to use them over ordering directly from manufacturers or more niche retailers.
I saw a post recommending to complain to Amazon, so I did, via their online chat to a CS rep. They amended the shipment I complained about and I got it the next day, and since then, most of my shipments have been within 2 days again.
My advice: complain to Amazon. If everyone did this, it would make a huge difference. If you don't complain, you are basically telling them you're fine with whatever delivery times they want to give you.