Again, this applies to any comparison of prose and comics, almost regardless of genre. I will allow that the world-building aspect of many fantasy stories (though not all, because many are set in a close facsimile of the real world) increases the relevance of the argument, but no more than for science fiction - so does science fiction also not work in comics?2. Nothing can beat the imagination. In a novel the writer describes things to you but your imagination fills in the blanks. So it's taylored to your personal tastes.
In comics the artist does that for you. And I must admit there are a lot of fantasy comics that don't do the books any justice.
This is the most compelling argument I've seen for fantasy working better in prose, but I still don't think it holds up all that well - except in the case of adaptations, which are almost always a lesser experience than the original because of the forced comparison to a prior expectation. So I'll happily grant you that existing fantasy novels work better as novels. But when looking at an original work of fantasy in comic form, there's no prior expectation to compare to, so I can't see why it would be better in prose if it was never intended for prose in the first place. In that case, your imagining of the world shouldn't get in the way, because the only world your brain has to work with is right there in front of you.
These two apply not only to all comics, but to all fiction. Recycling old crap is recycling old crap, no matter the medium or the genre. And if it doesn't come from the heart, what's the point of writing it? If someone doesn't like fantasy, they shouldn't be writing fantasy. And if they don't like crime fiction, they shouldn't be writing crime fiction (or any other genre you could insert).3. And this is important. I think fanatsy can work if you have a specific story to tell. Not just being a writer and wanting to throw your hat into a specific genre, which is what writers want to do. Not saying they can't. But I think alot of comics writers just don't like it.
4. It has to come form the heart and overcome the medium.
And I don't understand why it has to "overcome the medium" (unless you're talking about adaptations again). The medium is the medium. Any original work of fiction has to work within the medium. You only need to overcome the medium of comics if you're trying to draw in people who don't read comics, or push the boundaries of what comics are - both of which are noble goals, but not ones I think all good comics must attain.
You've got a good point with the art, but it's still a point that applies to all comics. Ideally all comics should have good art. If not, they're not good comics (even if they might contain good stories).5. Just get some good artists for the projects. Not the up and comers who really can't hold it together.
I also can't help but think that some of the folks claiming fantasy doesn't work well in comics haven't read much fantasy in any form. I mean, things like claiming, "the format for most every fantasy story- the hero goes on a quest," don't make sense, because it's simply not true. A sizable percentage of fantasy stories follow that formula (possibly one could claim too many), but it's far from "most every". It's just a common trope, not a defining element of the genre. It's like saying most every science fiction story involves space ships.