Kinda depends, I suppose. If your art page has its own specific "brand" that doesn't necessarily mesh with your comic, then keeping them separate might be worthwhile to avoid content whiplash for your followers. But for most artists their art and comic work are similar enough that they can "get away with" consolidating them into a single "brand". It sounds like this is the case here if you're re-posting the same content onto both pages anyways.
Other considerations are if splitting your follower base is worthwhile and what benefits the comic-specific page yields that your general art page can't cover. I think there could be some benefit for a series with a large fan base and/or for a creator with multiple series as people may only be interested in content for that one thing and want a place to gather and talk about it. For most smaller series I would think that managing 2 accounts would be more hassle than worth.
I typically think of separate accounts being more applicable in the case of, say, a youtube content creator or something that does two or more vastly different types of content. Say, Art content and Gardening tips or something. In a case like that the content is different enough that you might give your followers a bit of whiplash by having it in one place- the people who subscribe for art content may get put off by the gardening videos and vice versa.
