Very likely Power of Magick was inspired by GoM. GoM was probably on the scene first if I got my dates correct. Also remember that even though Corwin Hargrove released his books around the same time as some GoM books, he was not part of the Power of Magick group until much later (2020+).
Aside from Lucifer and the Hidden Demons, there is a surprisingly large amount of overlap between PoM and GoM. Plenty of their books rely on the same old Practical Kabbalistic and Solomonic magick inspired stuff. I would argue to say that PoM is just slightly more varied in some ways if you include the pathworking stuff, which really was kicked off by Lucifer and the Hidden Demons. GoM goes quite a bit further into Kabbalistic stuff, especially with their angelic magick.
As for similar authors, it is hard to say for sure these days which ones are similar to either of these. Like you said, a ton of the books these days (e.g. Mari Da Silva) are likely to be AI generated and consequently low quality. But if you want some books from the same vein as GoM or PoM, I could easily recommend Jareth Tempest and Tristan Whitespire. Their books are inspired somewhat by different books from GoM / PoM. Jareth has pathworking books which work through Raziel and from what I here, they seem pretty solid in terms of results. Tristan Whitespire used to be in the same groups I was in and he shared a lot of different stuff before publishing; from what I could see, lots of people got results through his free stuff. Both were in fact part of the groups I used to frequent and they had decent reputations for putting out good modern magic books. Mind you, these 2 started pushing out books before AI slop became a thing and I do not think they would endorse using AI to push out slop even today. So they should be decent if you want to avoid this stuff.
Mind you, a lot of people still have issues with the modern grimoire genre no matter how good / bad the books actually are. I feel like I gave the names of 2 fellow who are decent within the genre. The folks from more traditional backgrounds still like to shit on even the decent authors of modern grimoires, so I would recommend you approach their works with an open mind.
