It was shocking to me that it actually happened. We were only at 4.27, then UE5 hit. UE5 was a chance to turn things around and distribute large changes to the engine code itself. You’d find it advertised as the “game changer” (later sub versions too) just about everywhere. Except… It was just UE4.27 with its bugs and added experiments on top of it. Definitely just marketing. They didn’t refactor the old engine code as far as I noticed. To me this was most noticeable with the Slate / UMG system, I saw your response on that thread. That system was refactored over X sub versions breaking 2 things for every fix. The public response to UE5 of many was that they intended to stick with UE4.27 (even with its bugs) which is worrying. At the rate UE5 develops I’d currently expect a UE6 to launch out of nowhere using the same strategy. UE6 then being the same ape in new clothes. It would be disappointing.
I’m seeing a reduction of EPIC staff involvement over the years. I’ve heard many off the staff were fired but I can’t verify this. On the forums there’s never been that much staff activity compared to community activity but I can tell sh"t has hit the fan. That’s because they launched a bug reporting form on the forums, which only later turned out to only be monitored for Fortnite bugs. I talked to staff about it. The form was altered to a Fortnite bug submission format. There’s also a bot on the forums scanning for such bug reports, again, only Fortnite bugs get scanned (staff confirmed). As far as I know, our feedback on “just unreal engine” is not collected. Either way, the lack of communication between staff and community makes it look so.
Recently the button to report forum posts changed in functionality as well. Previously you could report a post and basically directly contact a mod on the forums. Now you get redirected to an EPIC page where you get to log in again and go through a report form process. Such extra steps are usually implemented to stop people from complaining and further reduce the amount of time staff needs to spend on problems.
In short, everything I’ve seen so far on forum developments points at staff reducing time spent on actual problems, and on collecting feedback. The community feels ignored. Fortnite is called the cash cow.
The UMG / Slate bug post I linked is a good example. Some bugs that were introduced were ridiculous. Like a broken getter function for a slider / editable text box value that would fail 100% of the time in any context. There was no test for it. On EPICs side, that takes 10 minutes to fix. On “our” side, the thousands of UE developers had to look wtf was going on and duckttape to see if there was a workaround to get base functionality on the UI to work. That is a LOT of time wasted and is experienced as insulting to all of us.
When prototyping yes, writing tests takes time and slows down prototyping. Once people work on a project for months and intend to release a large plugin or game, they don’t intend to switch engine versions halfway or use prototypes. The way I see it, prototypes just have no place within engine code. If people prefer rapid development without testing properly it shouldn’t be included with engine code.
Meanwhile EPIC requires that FAB products support the latest major engine version. As I remember from some agreement somewhere (perhaps EPIC Marketplace), they would even have to support the latest 3 major versions in order for the product not to be “possibly” removed from the marketplace. Yet, the latest 3 major engine versions can not be used to release a full game due to engine bugs. 
. Even FAB is experienced by many as a partial and bugged implementation of what it could have been. Browse to any page and look for errors on your browser console. Sloppy and lacking in features.