In Seagal's "hey-day" he was taking advantage of what Chuck Norris, Jackie Chan and Claude Van Damme were doing (and Bruce Lee before all of them) and it may have caught on for a short while. But Norris and Chan kept going and were successful whereas Seagal and, for the most part, Van Damme, faded away a bit, mainly due to the fact that Norris and Chan are genuine martial artists and the buying public eventually saw through the pretenders. Seagal is starving for attention and always has with his made up CIA stories, etc.
Here's a short clip of Norris opening up on his feelings about Seagal:
https://www.youtube.com/shorts/EczXT1Z-Enk
I wouldn't place Seagal and Van Damme in the same category AT ALL.
Watch this guy's review videos -- he seems to be a fan of Van Damme, and I can see why. You gotta admit, Van Damme actually knows martial arts. He's actually in shape, athletic, he can do the splits, he can spin kick. Action movies are always fluffy popcorn movie nonsense, but if you want a good action movie, I think Van Damme movies deliver. He isn't a pretender. It "looks" awesome on the screen, and that's the whole point of a fighting/action movie.
Now Seagal on the other hand, he's obese, washed up, mumbles all his lines, has bad dubbing with different voices for some of his lines, and he just plays patty-cake with the bad guys in his "fight" scenes, where his stunt double does all the work. I've actually seen fight scenes where they periodically splice in a second of him just moving, sometimes with a different background! (I'm not joking) It was the most ridiculous thing I've ever seen produced by an adult.
Seriously, he uses a stunt double to go up a flight of stairs, etc. He's pathetic. He's not even entertaining to watch from a "lets watch an awesome fight scene on the screen" standpoint. And his movies are awful, because to compensate for Seagal's lack of ability to do awesome fighting on-screen, he just shoots and kills lots of people on-screen, at least half of whom are completely innocent of any crime. He doesn't even make that look good either. He does "don't look shooting", no-scopes, sprays-and-prays, and flinches while firing wildly in any direction, somehow magically hitting people fatally. It's painful to watch.
Seagal pretends to be the protagonist, but he's actually the villain, in pretty much all of his movies. Van Damme is usually a great guy with a heart of gold in his movies. He's much easier to like.