Considering he was nominated for a Bram Stoker Award for best first novel for FEAR BOOK and received accolades for his followup novel WHIPPING BOY and his other horror genre short fiction when he was writing fiction semi-regularly in the nineties, I don't think his writing is an issue, per se.His days of relevance and interest have waned. Which, in some ways, is a shame. If he had not been as outspoken or as, well, dickish, he could still be a top tier artist. Not so much a writer though. If John Byrne had started off with zero artistic talent he would have never made it as a writer. But that's a matter of speculation.
His ALPHA FLIGHT, his HULK, his short BATMAN stint, the classic Spider-Man and MJ as Red Sonja vs. Kulan Gath in MARVEL TEAM-UP (in fact there's a few MTU and M2-in-1s one-shot stories Byrne worked on that are memorable), the LEGENDS mini that helped set up the DCU after Crisis... his AVENGERS stuff, his CAPTAIN AMERICA run with Roger Stern... there's a lot more than just the X-MEN / FF / SUPERMAN work.John Byrne will be remembered for the X-Men, the Fantastic Four, Superman, and being an asshole. Everything he has been doing for the last few years and for years to come will be an afterthought. That's what it comes down to. If you like his current stuff -- awesome. For the majority of the comic buying public it's more a case of "Is that all there is?".
But when you stop and think about it, most comics creators are predominantly known and beloved for a handful of works amongst their larger bodies of work, and seldom is it their latest efforts that always hold up as the best content they do. So it's really no big deal.
Karl... is part of Periscope Studios, which is the largest group of online comics creators in the northwest. I believe he was / is writing at Marvel most recently. I know he recently made news in August about selling his comics collection in order to afford adopting a baby who was born addicted to drugs. (Crack? Heroin? One or the other, I don't remember the specifics.)
Admittedly, I was banned from his website, but that was for a bet; how long would it take without resorting to bad language, or being too obvious about it? At the time, there was a thread on the subject of whether or not Frank Quitely's cover for All Star Superman, issue one, made Superman 'look gay'. What if he was, I wondered. What if Superman was secretly in love with Brainiac, etc, and just using Lois Lane as a beard? Bingo. The ban-hammer was swift.
Frank Miller and Alan Moore can get away with the occasional outburst; even Dave Sims sort of can, but John Byrne is at this 24/7, in a way that can only be destructive to his critical reputation, long-term. He was great on the X-Men, and Alpha Flight in particular (though he doesn't seem to like that) but now, he appears to prefer to see himself as a sort of on-line voice of truth, with well-thumbed copies of Walden and Atlas Shrugged on his bedside table. As if his career's been leading up to this. If so, I'm happy enough to judge him, on those terms.