It’s not that “transported to another world” stories are all power fantasies, but that the last ~5 years of what gets greenlit for manga/anime release has a lot to do with the mega-popularity of, I suspect, Sword Art Online in particular. The alternate world plot device itself is super old - I only had the realisation recently that the Wizard of Oz and Narnia are basically isekai.
Those are both good! In the same genre, I also like Koushaku Reijou no Tashinami (Accomplishments of the Duke’s Daughter), it’s the same setup but gets more into politics and economy and financial management, which isn’t everyone’s thing but as someone who enjoys e.g. Crusader Kings and Civilization games a lot, I enjoy the fief-building angle.
My friend has been reading through isekai manga and is slowly creating a list of zir favorites and other notable ones of the genre. The write ups have been pretty in-depth so if anyone is looking for more suggestions, here you go. Currently a work in progress because zie read about 100 isekai manga.