We see so many isekai titles because it is an easy storytelling framework. Stand in for reader gets transported to new world. Has powers so the reader can get that trip but also needs to have things explained to him so the reader can understand the world.
Further tropes are not without their reasons. Video game mechanics = a world that is very easy to navigate for the reader. Slavery = instant sympathetic companion who adores the reader um, I mean, the hero.
I say all of that because the worst isekai titles are the ones that don't try to do anything new and just plod along letting the tropes do all of the work.
The latest to make my poo list was one of the newer super farmer manga. I don't think it had slavery but but it checked a bunch of other boxes: Main with cheat leveling mechanic, Clueless about his own strength, Doesn't want to be a fighter, Pursued by cute, etc...
Isekai isn't bad in itself. One of my favorite anime is The Twelve Kingdoms but that was way back before it all blew up.