I agree with your points, but look at the downsides as well.
Taking UE as the example, it started as a copy of the Quake engine. And after time they added more features to it, aside tools for content creation.
Meanwhile, id completely abandoned the idea of baked lighting and came up with Doom3. First game with fully dynamic lighting and proper shadows - real progress.
It then takes some time until UE adds those or similar features too, and even more time until those features work robustly. (Remember character shadows on wrong places in first UE games featuring shadow maps.)
Meanwhile id abandons the idea of fully dynamic lighting and goes back to baked, but now they show individual texture on every surface in a huge open world.
Crytek shows big progress too with their completely dynamic lit huge open worlds, coming up with SSAO and first dynaimc GI.
UE also adds similar methods to compete. Many features, some incompatible with each other, but it works and grows.
But efficiency suffers, it becomes bloated and out of date, and unable to compete custom engines on current gen consoles, they decide to go public, target indies, and also for the first time they also show real progress with TAA and PBR too.
Nothing wrong with this. But now adding RT it is again just one more optional feature (or many) on top. The alternatives still need to be maintained. Still nothing wrong - they have enough manpower to do so.
To see how wrong this might be, you need to compare it with something like Path Tracing where a single algorithm calculates all lighting. In contrast, in games we have dozens of methods, each faking just one piece of the puzzle, each having it's own perf cost that sums up.
Now i don't say PT makes sense for games, but custom engines have it much easier to do things differently, implement new methods while abandoning old ones, coming up with more efficient results, achieving progress.
So i guess the trend will continue we will see new things in custom engines first, while UE ofc. makes it easy to enable RT effects for many other games.
Ray Tracing in UE4 is the same way, and I do not see anything bad about it. Rather normal as I see it.
Yeah, but normal / state of the art is not progress, it is the result if it. That's why it is important at least big studios have their own engines, and using middleware only for things where current state of the art is good enough for them. (Either this or having more competition in the middleware segment.)
I don't mean UE would be bad in any way, and sorry if my historical example is not accurate.