My view is that he has his own methods which clearly work for him, and he has achieved a level of fluency that I can confirm is quite good (I speak several of the languages that he does), so there's something there.
I think his general prescriptions are correct and track with my language learning journey. As to the specific prescriptions he makes, like the use of mini-stories on LingQ, I've not found them to work for me. Or his prescription to read and listen a lot before attempting to speak -- I don't agree with that, though it seems to work for people with his cognitive style (i.e. more introverted rather than extroverted). I don't think either of these detracts from the points I made above though.
As for self-published books, I'm not sure I have such expectations of self-published authors that I would be affronted if they didn't deliver on their promises, but I haven't not read anything by him so I can't assess.
He has a business (LingQ) but I don't get the sense he's really peddling it any more than any other business (most YouTube creators do the same -- self-promotion on YT is just part of the game), but I guess perceptions differ. Again you're entitled to your opinions, but I do feel they are rather strong compared to my own assessment.