You guys are right.
He launched an "offspring of a pterodactyl and a comet came hurtling out of the darkness at the far end of the cavern. My eyes had adjusted enough to see a dim oval of reddish light that outlined a heavily cloaked figure--Cowl, standing in his own gate.
Master! Vittorio cried, his voice slurred.
"Look Out." I screamed, and thrashed behind me with my arm as I ducked and lurched ot one side, trying to sweep Lara out of the flying thing's paths I did. It missed us by inches, but we got out of the way.
Then, on second pass:
Lara dumped me at the mouth of the tunnel, and I took a couple of steps back in, checking the smooth tunnel walls as I shook out my shield bracelet. That demonic flying thing of Cowl's banked around for another pass.
I still say it's possible for Cowl to ride the thingy if he wanted to, but it didn't happen like I had thought it did. We didn't see exactly in the text what happened when the flying thing banked around for another pass, other than that mention. It could be possible that Cowl sent it to quickly fetch Vittoro, Cowl hopped onto it to get to and protect Vittoro, or it plainly went in attack mode for another pass. There is no mention of it after that last sentence and the bombs explode some few seconds later.
It's weird that Cowl didn't do more to inject himself in that fight than he already did with bringing in the SuperGhouls, etc.
Now, to tie the Deeps in with my main theories.
Assuming my theories are true regarding Murphy/Mab and Marcone descending from Harry and Murphy, then Cowl at that point had an operation going on in the Deeps that could perhaps unintentionally wipe-out Murphy, Marcone, and Harry all in one fell swoop thereby sparking a series of temporal instabilities that could/would have enormous feedbacks on reality. However, it the theories are true, then there must also be great inertia in preserving said 'history' from being tampered with. This is my idea of what Team Bad is trying to do, Cowl and Outsiders are trying to undo Murphy as Mab. And, they aren't just attacking in one time to do it, nor in just one reality.
I do realize though that the main assault was placing Vittoro on the throne or perhaps freeing Lord Raith or something similar.