Oh, better believe they iz waaay different. I played the UE5 one shortly after it dropped, downloaded it and played it for a week without much interruption earlier this year. And now the UE4 one, for about a week now. UE5 feels like a veeery condensed demo, while UE4 feels like a rather advanced playtest of an actual game. UE4 has loads more of mechanics, NPCs interactions, and the whole setting feels waaay more alive & vibrant than UE5.
But UE4, which I have been playing non-stop for the past week or so, is admittedly also a helluva lot more buggy - like not saving clothing selection on close game, merchants not restocking properly, vessels not spawning thus locking you out of certain cosmetics (as in, even the very first fucking one was missing couple times - the one with the cute punkish haircuts for human form), etc etc....
I still do agree with your idea 110% though, a combo of UE4 build & UE5 build would be most awesome. If map was twice as big as in both the "demos", with twice the number of quests and maybe a few more sidequest POIs & random encounters - and twice the number of sex scenes (as in like, ~30 total, plus the ability from UE4 version to sex up random NPCs strolling around the map), AND most importantly, a player camp with some sort of harem thing going, be it caged slaves like the inquisitor lady or "companions with benefits" like Ahmes -
it would already be a total blast 
.
And with regard to the sex-cut-scenes that don't have interaction, maybe the devs should take a few pointers from
Subverse. I know, itz an oldie..but also a goodie. It has A TON of very decent sexy cutscenes for a UE4 game, feels more like a 3D-porn movie with mini-game interludes than a real game at times. But iffen you implement sexy cut-scenes in your game, as they did a lot in CI's UE4 version, I think this would be the better way to do it.
Subverse has tons of sex-cut-scene material (I mean the whole game is what, 60-something gigs, and like at least 80% of that is just video files), all properly edited and showing the action FROM PROPER ANGLES!
It's my one & only gripe with the sex in this game - why on frikkin earth would you go with such
dumb-ass, useless and un-sexy camera angles, that show
absolutely NOTHING of the action?!? Some instances (in both versions) it's really nice hardcore and shows everthing in awesome furry detail, but at other times iz almost like watching a softcore movie on late night public TV, where you get teased a lot with pretty bodies, but ultimately don't get to see no cuntz or dikz.