You can shit talk the series, but it's the first isekai I've read where the MC has legitimate concern about his pet he was suddenly pulled away from.
WHAT ABOUT ALL THE CUTE PETS, TRUCK AND/OR TRAIN-KUN?
Plus there is quite a few others that are far deeper into wish fulfillment than this...
Shingan no Yuusha is pretty much straight male fantasy wish fulfillment, but at least it's funny.
Isekai Meikyuu de Harem is borderline rape male power fantasy.
I can think of half a dozen that are worse than this, but really...
None of them compete with Mushoku Tensei. It's just disturbing when you really think about the plot, especially what trash the MC is, yet it's one of the most popular isekai available.
Point is, "wish fulfillment" goes plenty far. In some cases, too far, and yet the series keep going. The novel version of Daydreamer is way more disturbing than the manga is, but they still felt it was worth making a manga out of.