@Petnavis
Exactly. Not all premises involving kidnapping/stranding/exile/time travel or anything else of the sort are isekai, and not all of them are subject to the narrative problems specific to isekai.
@HolyDemon
Aside from what Petnavis said, it's important to remember that all tropes—especially major ones—are tools with an opportunity cost. Using them just to take creative shortcuts cheapens the experience, which may be fine in a parody or a decidedly schlocky romp but feel unnecessary in an actual solidly written narrative. Amnesia is a great example: if you build the narrative around it and use it to subvert expectations and/or gradually reveal plot-critical details, you get something as interesting as Memento or Mulholland Drive, but if you just use it as a device to create artificial drama or conveniently escape a difficult plot situation in an otherwise serious story, you've damaged the integrity of your writing.
That being said, I don't think The Faraway Paladin's use of isekai tropes has been a pronounced liability thus far (if anything, the wyvern suplex is a better candidate), but it's hard to argue that it's nothing more than a creative shortcut completely unnecessary in a story like this, and was most likely put there just because it's trendy.