This is just a quick question from a thought i had, the 2nd beta for Insurgency: Sandstorm began the other day and it's pretty good, though there are what feels like frame pacing issues, stutters and frequent crashes to desktop, at which point i realised, most games using UE4 feel... weird, besides the occasional technical issue there's always something annoyingly wrong about UE4 games i play.
MotoGP2018 is great, though some tracks cause the frame rate to stutter, the anti-aliasing options are terrible and rain causes weird ghosting.
Tekken 7 is possibly the cleanest UE4 game i've played, though i had to disable some ugly blurry filters using config edits, online matches lock up during connecting, rematching in private matches takes way too long (but that's probably a dev issue) and it crashes to desktop occasionally.
PUBG has well known optimization problems, so much so that the devs are currently running updates named "Fix PUBG".
Fortnite is weirdly demanding for its graphical style, i can run it no problem but more than any other game it causes my CPU fan to go nuts, and has slight input latency.
Astroneer isn't finished, but to be fair most games arn't these days, and is full of technical issues.
Gears 4 is very good, i thought it was hilarious that because my friend was playing on his Xbox that for some reason his animations had to run at 30fps :P.
We Happy Few is... We Happy Few...
There are of course loads of other games, and every one i've touched has had something about it that needs fixing or adjusting, is it modern development techniques? The rise of higher budget indie games? Are there inherent issues in the engine, similar to how most Unity games don't perform the way they probably should?

Anyway just a thought i had, any similar feelings or am i seeing things i shouldn't?

I think your issues more pertain to the games and their developers.

Looking at your list the ones that you report to run poorly are from small studios that started in early access (We Happy Few, PUBG, Astroneer) and the ones that run great are from long standing professional AAA studios (Tekken 7, Gears 4.) You've got some exceptions in there like Fortnite, but that game is running 100 people simultaneously on a large scale map, UE4 wasn't built with that type of game design in mind from the beginning and Fortnite has been a great usecase for Epic to find and work on those issues (input latency is one already noted by them, which has subsequently trickled down to improve other games like Tekken 7.)

I think it's just more noticable because of how widely used UE is by any studio at any experience level because it's entirely free until you start making an income from your product. Naturally this is going to result in a lot of different people with varying levels of competency in game engine use.