Wrong. In 90% of garbage Isekai anime, removing the Isekai portion would do little to change the plot, while in the best Isekai, it is inherently required and cannot be simply replaced with a set-up beginning motivation a la the start of Bleach.
The point of an Isekai is that a character is displaced from their own world and thus their interactions with the new world differ to the native inhabitants. It creates an interesting diversion from the path of the world. Even Subaru, weakass that he is, changes the path of his world with relatively simple changes. If there are no stakes or important changes we lose the point of the entire Isekai, and it becomes a bland power-fantasy. Bland power fantasies can be fun escapism, but in the longrun are tiresome.
SAO abridged for example, does something interesting. While the world is digital and essentially fake, the characters themselves are important and their displaced situation. Kirito, who is a loser IRL, gets to be his 'dream self' in the game, but the reality is that no-matter how many swordskills he has, his social skills and understanding had to change for things to matter. He had a long and varied character arc of him reaching conclusions or almost getting it, only to have it taken away again and again until he finally reached it in a climactic battle. he then continued developing this newly found conclusion, on slow burn and realistic takes of teenage drama (played humorously). By the final battle, he put aside his own desire to remain awesome in the game and freed SAO's players from the game and it's fake life. The original SAO never quite gets this unfortunately.
this is getting boring