This has always been my gripe with internet buzzwords and phrases. A lot of the time they're invented for a legitimate thing but once it's out there you can't control it and people will misuse and misinterpret it (often for their own clout), and then the use in the original context becomes discredited.
I think if you read the Sealion comic as specifically a parody about the alt-right, it's alright, but the moment you start talking about "sealioning" as if it's a generalizable logical fallacy or something it completely falls apart (I doubt it was ever intended to be read that way either). It's about as serious of a criticism as putting the other side's position next to a crying wojak.