Only if you view comics solely as the big two.  Mazzuchelli first branched off into art comics in the early 90's with Rubber Blanket, and he's since been going strong in that channel (although he hasn't had a major release since "Asterios Polyp" won a slew of awards back in 2009). 

Travis Charest comes to mind for me. I remember seeing him do a Flash annual, and thought he was going to be hot. I don't remembering seeing much after that, though a quick google reveals he's still out there and active.

Edited to add: I recall the colors being quite complementary to the line art.

But, yes, I wouldn't mind more too!

 David Ross exceeds the 12 issue maxim but he is seriously under appreciated he was one of the few artists I followed from Marvel to Valiant 

12 issues of Camelot 3000, the Killing Joke and a few odd issues here and there.

The rest is a few Judge Dredd stories (which were not full comics), and stuff like annuals where he draws a pinup or a 3-4 page backup story.

That brings to mind Adam Hughes too.  Not sure how many books he did (loved his fairly recent BETTY & VERONICA mini!) because I think a lot of his work was later Image stuff that I missed, but we all know him from his cover work.

Just like Joe Sinnottt and Tony De Zuniga were great pencilers (or penciler/inkers) but they shifted their focus to inking for the last decades of their careers, or Larry Hama and some others became editors, Bolland, Hughes, and Art Adams becoming mostly COVER artists is a legitimate career turn.  They certainly didn't disappear like Mazzuchelli or Plunkettt--being a cover artist seems like the most high-profile job in comics.