Not comics, yes. But it's only "debatable" that they're not better than Watchmen in the same way it's "debatable" that grass tastes worse than vanilla ice cream or a foghorn is more musically interesting than the Jonas Brothers.Uh, no. The Iliad and the Odyssey are not comics. And it's certainly debatable whether they're better.
Which is to say, I'm sure you can find people who will argue the point, but it's probably best not to take them too seriously. Watchmen is more fun, maybe, easier to read, certainly, preferable to while away a lazy afternoon, perhaps. But better? No.
I don't think it detracts from the the comic to suggest it falls a little short, by any reasonable standard, of one of the longest-surviving and most durable works of literature in history. Call me in 2,000 years if they're still interested in making a movie from Watchmen, and we'll talk.