Frieren is not an Isekai though.
Without having seen this: Most Isekai are purely power trip wish fulfillment and they are diametrically opposed to having stakes, yet act like there are stakes. This makes them terrible. Don't make the protagonist OP, or make the protagonists OPness so over the top it becomes funny and the Isekai can be good. There, I fixed it.
Also: don't do slavery.
Also: don't do slavery.
if you're gonna do slavery, kill the slavers and free the slaves
John Brown isekai
https://www.royalroad.com/fiction/57505/his-soul-is-marching-on-to-another-world-or-the
Fair, but I don't trust these authors to do that right so they best just don't do it.
My main problem with Isekai is not that MC might be OP, but rather that their character is nothing unique. You always have this stupid "Ah, you are already mature with 15!" line, which is a bad excuse for sexualising someone who is underage. And then you have always a harem, because it is common to marry 93483929248432 women! MC is of couse stupid as fuck and never get it if a girl is intereated into him (its of course male). Everytime the same shit over and over again.
What makes the problem worse is that theyre power fantasies written specifically for bitter straight men who think they were overlooked. The audience is basically otaku/incels, which means the wish fulfilment fantasies are always horrible shit like owning slaves or getting back at all the evil women who wronged you. Also I don't think there's much of a difference between the average isekai and the run of the mill generic fantasy anime anymore, it seems to me that they are the same thing for the most part. The only difference is whether the guy was a loser before dying irl or if he's a loser because his fantasy power sucks.
I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy:
