My situation is similar to yours (except I avoid even the free trials) with similar shipping times. I do have a primary warehouse for my metro area about 5 miles away in my town. I think items that are in that warehouse or on their way to getting replenished arrive as quickly as ever while everything else takes longer. I'm fine with that but I'm also looking to get even further away from using Amazon after some poor recent experiences.
Without prime I still order from them more than I feel good about, but only ever opt for the free, slow, shipping.
I’m at something like 30% deliver relay in 2 days, 40% deliver in less than 5 days, and 30% take the full five days.
combining your experience with my own, really sounds like they’re losing it.