It's starting to feel repetitive as I read more and more novels about it
You might as well say that "adventure stories" are a stale genre. There is a theory of literature that all good adventure stories are essentially the same – "the hero with a thousand faces". It is all about taking some ordinary person to a fantasy land where they hero up, before (usually) going home again. That idea seems to fit everything from Gilgamesh to Star Wars to isekai stories. The trick is just to write it well enough, with enough new-and-improved characters and plot points, that it is interesting and entertaining one more time. Does it matter how the hero gets there, or gets back? Isekai is just a way to do that.
Of course, the isekai approach is not exactly a recent invention, either! I remember reading "A Princess of Mars", written in 1911 by Edgar Rice Burroughs, to be serialized by a magazine. Yes, that is 112 years ago, but I would say that it could be placed in the isekai genre of serialized fiction. Whatever you want to call it, the idea is to place your modern-world human protagonist in a magical world that mixes inhuman sword-fighters with beautiful human princesses. It is easier for the writer to work with a modern human character, and easier for readers to identify with the protagonist. Of course that has been used for a century or more. It just works too well! Don't expect it to go away soon.
On the other hand, the isekai genre suffers from tropes, cliché, and copypasta that get recycled by authors who rely too much on an easy template for writing, and fail to make it original. Please let truck-kun retire, skip the goddess's white room, ditch the summoning circle, and don't mix isekai with litRPG every time. It is much to late to rely on all those once-useful elements, even if you try to subvert them.
That gets repetitive. What about a world with swords but no magic? Or magic but no swords – i don't know how that would work, but it would have to be original! What if someone just finds a "door into another world", or some such? Isekai-lite, but repeated less often. Or a magic book. Fairy rings, anybody?