I don't think it's a downgrade. The iPhone 5 design was probably already approved by Jobs before he passed away.iPhone 5 was a downgrade respect iPhone 4.
While 5 was one aluminum case the 4 was a multilayers case in glass and stainless steel.
When you try to open a 5 you need to dissembled whole device, on 4 just slide the rear glass panel.
iPhone 4 was the most designed iPhone ever, with all its issues.
Compare iPhone 4 design and Mac Studio and you could understand how the old Apple Design Team add value (value, not cost, Apple's prices aren't better today) on them devices.
As for ease of disassembly, since when Apple cared about that? Apple also changed the screws of the iPhone 4 from regular phillips to penta-lobe mid-cycle. That's how bad Apple doesn't want you to disassemble the device.
I do agree that the iPhone 4 design is great. But imo the iPhone 5 is not a downgrade. It's the natural progression of Apple.