A large chunk of UE5's value is being able to plug in technologies from third parties. The problem with this however is that third party technologies are out of your control when it comes to modding, you can't provide the userbase with access to anything that uses those technologies because you don't have the license for them.

I guess Crimson Desert is the first game on an all-new engine in a while?

Yeah. Then there's CDPR with Cyberpunk. I think the most impressive engines that exist currently are rage9 (rockstar) and Decima (Death Stranding/Horizon Zero Dawn). Special mention for Ubisoft's engine too Anvil, which is a seriously amazing technical marvel wasted on making the exact same Assassin's Creed gameplay over and over and over again.