Steven Seagal is just a hack. He's not legit, he has never proved himself in competition, which is what counts, and the one time he did fight he got choked out and pooped his pants.
Aikido is a joke. It "works" against people who have no clue what you're doing and you take them by surprise, but anyone who is actively resisting and has decent physical prowess will expose the techniques as jokes. They're just not battle-tested because Aikido doesn't spar. Their techniques are mostly theoretical one-time surprise uses.
Arts like Judo are much, much more effective, proven and practical.