It might not be the engine. Some companies just don't care much about optimization when they can just tell their players to buy better hardware.

Take GTA5 for example. It had a notoriously long load screen when starting up. Ranging from 2 minutes to 10 minutes depending on the read speeds of your storage drive. A modder ended up finding the problem. The code to load up the items in the game opened and read a file, but there was a bug that caused it to read through the entire file for each item loaded. The file was being read thousand of times. The modder changed one line of code and the loading time was reduced significantly. This was a bug that plagued GTA5 for years, caused by a single line of code, that the company didn't fix because their fix was to buy better hardware.

UE5 is just a tool. Developers are the ones who are responsible of the game performance, more than Epic.

There are some problems that plague UE5 games like transition stuttering (moving from one zone to another) among other things, but overall I couldn’t blame the engine when the ones who use it are not me, but the developers themselves.

Same flak for Rocksteady and Batman Arkham Knight. They used Unreal Engine 3 instead of 4, and ran like crap anyway.

Studios and publishers will happily pay UE fees if that means pushing the game on schedule than wasting 2 years creating an engine from scratch that can’t resell or reuse (there are exceptions , tho)

My impression of it is that you can achieve good performance in UE5, but you won't be using the newer tools for that in most games. Many of the newer tools, like Nanite, comes with a large up front cost, but scales well after that. So you can make a beautiful game that runs stable 30 fps with some effort, but reaching 60 or 120 is trickier when using the newer systems.

Since there are so many different systems in Unreal 5 it's also a beast to understand. Understanding a system is in many cases a key to performance optimization. Performance is also something that spans most disciplines, adding more people that need to understand it.

UE5 is targeting capabilities of newer hardware, compared to UE4, so it tends to push the limits more.

UE4 has had a lot more time being refined than UE5, so it is understandable that it performs better.

Making a game look nice and run well on newest hardware and do the same for lower end hardware takes a lot of effort. You may need to fall back to older systems with different visuals and spending time on getting it to look similar enough. Sometimes two systems may even not be feasible to switch between, so then in most cases the newer system with better quality takes precedence.

I could go on about this at length but I mostly want to communicate that people underestimate how hard it really is to make a game that is a good investment, fun, beautiful and performant. There is always a balance to be struck.

I heard from a game dev that UE isn't an engine, but a framework. That means it doesn't give you optimized, opinionated code, but gives you more "freedom" - yet forces each dev team to optimise by themselves.

Which they either don't or do poorly.

unreal has, at least since the 2010s, an engine that focuses on AAA looks and advanced features. 5 amped that up with nanite and other gpu stressful tech.

I personally found UE4 to be a bloated dev environment, but ymmv.

My uneducated guess is that most of the time spent on any optimization has to go to console ports. With PC you can just tell people to get a better PC, but with Sony and Microsoft they will straight up refuse to sell your game if it doesnt run well enough (see: CP2077 on ps4 or BG3 on Xbox).

Hard to say whether it’s the engine or not when playing specific games but seems that Lumen has a big impact in the engine at least.