There are a few names on the list that I don't believe have done enough writing, much less good writing, in the last 25 years to warrant being on the list.

2 of the 3 you give the unqualified nod are 2 of those I vehemently disagree with and would put on the most overrated of the last 25 years. One is a one note pony, almost everything he writes has the same thematic underpinnings and all his characters have the same authorial voice (not character voice, those are nearly non-existent drowned out by the authorial voice) and are mostly interchangable except when he ventures into a certain genre, and the other's best work was early in his career and has been riding the coattails of that stuff producing flat cardboard stories filled with underdeveloped flat cardboard characters that are part of his "grand big idea" about the nature of fiction and spouts a lot of bs but really never ever says anything.

As for what is under consideration, SyFy I think looks at the bigger mass pop culture field, so their lists focus on those who have made in an impact in the wider pop culture of the last 25 years regardless of genre or subject. Clowes, Bagge, etc. are exceptional writers to be sure, but I don't think they hit the SyFy pop culture radar. I think the also focus on creators for whom the bulk of their best known work is in the last 25 years.

-M

It's a decidedly mainstream list.

I'm sure who I might add that isn't there. I don't do a lot of the navel-gazing brand of indie books.

I guess I understand Geoff Johns being there, though I think he's the worst kind of fanboy writer.

I'm not a fan of Jeph Loeb, but I don't actively dislike him.

I've never read any of Gail's work. I found her personality so toxic and annoying that I couldn't bring myself to buy anything she wrote.

I'm pretty sure that @mrp is talking about Ennis and controlling for his War books. I'd personally put him in my top five favorite comic book writers of all time. Unless he's talking about Ellis...who might make my top five and would certainly make my top ten.

I've been indifferent to most of Morrison's work in the time period. Basically I find that when he hits, I love his work. When he misses, which for me is about 2/3 of the time, I hate it. But I certainly understand why he's there.

Yes it was Ennis, my problem with him is he has 1 story, when I read his Shadow I had read it before in Punihser and what I had read of Preacher. When I read his Red Tema, I had read it before in Preacher and Punisher and Shadow, when I read his Punisher I had read it before in Preacher. The lead characters are interchangable. The thematic underpinnings of the story are the same with only minor variations for plot. The supporting characters are the same tropes story after story, the pacing is the same every story, the structure is the same, you can predict when his polt turns are coming based on what has happened plotwise leading up to it every time, and for me, can usually predict what the tematic nature of the plot turn is going to be regardless of details of the plot itself just about every time. He has an outline, a formula, and he follows it every tome he does a story in the same authorial voice every time. So while I get the love for Preacher even though I didn't like it, he hasn't done anything but regurgitate the characters and themes of Preacher in any of his work outside of his war comics. To me, that formulaic regurgitation excludes him form the list of great writers. He's competent, he had one very good story in him I didn't like, but outside of that he has been plowing the same field over and over again throughout his career.

Johns and Loeb were two other candidates for my Most overrated list. Johns is the Greg Land of super-hero writers, he pretty much lightboxes the work of those who have gone before him and presents it as his own. If you look at anything, and I mean anything he has tried to write on his own when he isn't standing on the shoulders of the giants who came before him, it is terrible, devoid of ideas, and hamfistedly executed. He's the perfect fanboy writer regurgitating the same thing over and over again with only the lightbox illusion of change and appealing to the hardcore fanbase, but that is pretty much the textbook definition of hack not greatness.

Loeb has benefitted in his career turning in some weak stories made great by fantastic artists doing tour de force work and gotten the credit for their efforts propping up his stories.

As for Morrison, I have already said that once he hit American mainstream comics he became the Dan Brown of comic book writers, essentially creating an interesting character or two to take you on a guided tour of other people's ideas he cribbed from extensive reading of esoteric material, and then about 1998 or so he forgot to include the interesting characters part of it. If you've read the stuff he's cribbing from, the ideas are pretty much verbatim from them, they are just esoteric enough the typical comic book fan has never encountered them before so they seem wild, fresh and original. They're not.

-M

Don't think it's for superhero comics, cause Aaron, Brubaker, Lemire and Azzarello best works definitely are not their superhero work. Vaughan probably neither (he's on this for Saga and Y, I guess?). Stephenson has done primarily Lumberjanes which is not superheroes either (great title though).

Don't know Jody Houser and can't find little about her  (an adaption of the Orphan Black TV-series?). Same for Telgemeier.
Definitely not a fan of Jeph Loeb. I haven't read anything by Palmiotti that would put him in a Top 25 list (don't actually dislike the things I've read, but there are so many better writers around).

Kinda missing Kieron Gillen (Journey into Mystery, Darth Vader, Phonogram, Wicked and the Divine etc.) and Matt Fraction (Casanova, Hawkeye, Iron Fist etc.) here.
Personally not a fan of Kirkman, but the success of his series probably should have earned him a spot as well. Same for Bryan Lee O’Malley.

Peter Milligan not making the list invalidates it. His work is better than most on there.

Also, I know it's mainstream but Bagge? Ware? Satrapi? David B? Clowes? Cruse? The Hernandez brothers? Bechdel at least?

Milligan, for me, is a bit like Morrison.  Except his hits are much fewer and further between.  I did like Skreemer.  I liked Shade for a while, but then I got bored with it.  I thought his Hellblazer was readable if uninspired.  

Other than that I find him mostly unreadable.  And Enigma, which seems to be the big book for him, I find utterly unreadable.