Well, I'll try to answer in parts to perhaps alleviate a little of your bad feelings about HTML games.The interface just feels awkward, since 90%+ of my AVN collection is Renpy. That's just what the vast majority of AVNs have been made in since 2018 or so (though some new ones still use Unity, Unreal, HTML, RPGM or some weird custom one). As an example I tend to save at every choice (makes replays and seeing alternate paths easier), so if there's lots of choices it could have hundreds of saves, which is easy in Renpy but for HTML I have to make a folder and put saves in that, as there's only 9 (iirrc) save slots by default, which don't have preview images so unless I make a long-winded (but still limited to 256 characters due to Windows) name with the description a particular save can be hard to find among hundreds of them if I haven't played in awhile. Replay gallery? Renpy often has it as an extra feature but I've never seen HTML AVNs with that (so the work-around is save before every sex scene too, I usually put those in their own subfolder in the save folder). Wanna replay a different way and ctrl+skip dialog you've already read? Not an option with HTML, so it's alot of scrolling/clicking. Being lightweight does have it advantanges I guess, but also it's drawbacks. Out of 1400 AVNs in my collection there's 3 that are HTML that I keep up with, maybe 50 or so RPGM and others (mostly from 2017 and before), the rest are all Renpy.
- The HTML game interface is as customizable as the developer wants it to be. Some devs don't invest much time in this and make it seem like most HTML games are limited in this sense. But they are not.
- The number of save slots is also customizable. In my game, I set it to 15, but I can set it to much more if I wish.
- As for the replay gallery, perhaps you haven't played my game yet, as there is a fully functional replay gallery, exactly like in renpy games. You can enter the gallery in the left side menu and replay all the scenes already unlocked. And yes, the gallery is persistent between playthroughs as long as you don't clear your browser cache.
- As far as fast-forwarding dialogues is concerned, it is also possible, although not as conveniently as holding ctrl like in renpy games. Just use the "end" key on your keyboard to advance to the end of the page where the options to advance are located.
With all that said, I don't think you should stop trying good games just because of the engine in which it is made. But that's just my opinion.
I hope I helped clarify some doubts.