Those were two separate concerns - the idea about what qualifies as an action movie is one that's definitely going to be harder to parse than the likes of horror or Western (the current rule seems to be relying on whether a film is classified as a certain genre on IMDb more than anything else, which I grant is at least some kind of concrete qualifying system). The remark about Under Siege is obviously more subjective and mostly to do with me being underwhelmed by the Seagal movies I've seen to the point where I found it genuinely surprising that one of them could get in over any Jackie Chan movie, especially considering Chan's commitment to doing his own stunts and constructing elaborate set-pieces to that effect that stick with me more than almost any action scene in Under Siege (the main thing I remember about an action movie should be the action, not just the villains hamming it up).
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Iro's Top 100 Movies v3.0
I really just want you all angry and confused the whole time.