I don't think Malone's skating is all that bad. It's not great but it could be worse. As far as Comeau or Megna go in a 4th role capacity, I'd definitely give Malone a shot at supplanting one of them. Neither of those guys are world beaters.
Comeau is a lot better than Malone, and while he would probably be more suited for a 4th line role than Megna, we could find much better options if we really wanted to bring in someone else for the 4th line.
I wouldn't assume JR likes Megna though. I like him, this board likes him, but he's still a pretty fringe guy and it's possibly JR doesn't see him on the team this year, especially in a 4th line role. He's more of a call up when injuries hit the top 6, imo.
In an ideal world where we would get another top-6 winger, that's exactly what Megna should be. However, it's not an ideal world. Malone being a lefty is nice, so we could run with Malone-Goc-Comeau with the lefties on LW and righties on RW, but that's about all that's enticing with Malone.
I like Whitney but he really fell off statistically last year. I'm not sure he's a better top 6 option than what we already have and I know that's saying a lot, but still. Father time catches up to everybody and it seems to have caught up to Whitney.
IIRC, he got pushed out of Dallas's top-6 last year, so that's why his production took a big hit.