I wouldn't defend most isekai (and I actively avoid most of them, other than villainess isekai), but I find them interesting as a phenomenon. One cultural aspect that I think is interesting is that Western readers spend a lot of time trying to decode the secret meaning of the stuff they read, while in East Asia they mostly don't really give a shit. If dudes want to read 30 identical light novels about a dude who is immediately overpowered and has four waifus, they will produce 30 of these novels and then give them 30 anime adaptations until the money runs out. Chinese fantasy novels sound the most extreme -- you'll see plots where a dude kills literally millions while having a harem of twenty. (Killing every member of a clan because one of them wronged them is a common reason for mass murder.) Thinking that your leisure consumption needs to be virtuous seems like a Western virtue.

FWIW, the female-led isekai have the same age gap dynamic with the genders reversed. You don't usually get actual harems (because that would be slutty, I guess) but you do get five guys who pine after the female lead because she's just so wonderful. This the level of self-indulgence that gets Western audiences to complain "she's a Mary Sue". But the core audience doesn't give a shit. Of course she's a Mary Sue -- that's what they're paying for.

This leads to a lot of garbage (most isekai, for example), but it leads to a big pulp fiction market that doesn't really exist in the West anymore. The closest is YA, but even the discussion around YA has a lot of anxiety about whether it's virtuous. You also have many other fringe genres like Western litrpg, but that is a pretty small publishing market. Re:Zero or Reincarnated as a Slime are closer to Harry Potter in their cultural prominence in Japan than they are to Western litrpg.

Mushoku Tensei has a weird vibe around it that makes it seem extra-sleazy (the author feels like he's indulging in something), but in a way if you are going to tell a reincarnation story you're stuck with it. What's the alternative? The lead who is in a 17-year-old body dates a 40-year-old? That usually ends up worse -- that's you end up with the "it's okay that she looks 12 because she's a 1000 year old demon" characters.

The only light novel I've read directly is Tearmoon Empire, which is basically "the French Revolution, but a comedy". The main character is basically Marie Antoinette, and after getting beheaded she gets a chance to go back and redo it to avert her fate. It avoid all of the tropes. Otherwise I only know them from their anime adaptations. The Executioner and Her Way of Life is about someone who's job it is to murder isekai protagonists, so it's less trope-y. The light novel for Oregairu, which isn't a fantasy at all but instead about high school, is supposed to be very good.