Pedantic
Legend
The best gamelit/progression fantasy does away with the isekai premise. It's mostly a vestigial framing device, and primarily allows the author to get away with making up new systems late in the game on the basis the protagonist didn't know about them yet.
Then they have to figure out what percentage fantasy technical manual to story they want to be. It's a genre defining feature that you're expected and encouraged to do elaborate, detailed system exposition; at the extreme end you have something Andrew Rowe's recent Edge of the Woods, which I'd put at about 10% plot to 90% fantasy science textbook. That's very much a selling point for the book's audience.
Then they have to figure out what percentage fantasy technical manual to story they want to be. It's a genre defining feature that you're expected and encouraged to do elaborate, detailed system exposition; at the extreme end you have something Andrew Rowe's recent Edge of the Woods, which I'd put at about 10% plot to 90% fantasy science textbook. That's very much a selling point for the book's audience.