would keep belial. He allows the deathwing to be troops and also you still get the teleport homer if your 3 bikes get killed turn 1
The use for Belial is to Deep Strike away from any Teleport homer because of the pinpoint accuracy
His homer is kinda useless as
ALL Deathwing Assaulting units have to arrive on the
SAME turn (clearly stated in the codex), so if he's not on the table the turn the
DWA takes place, it's useless.
You should group your two 5-man
Tac squads into a 10-man unit that you combat squad if needed, just in case you get the Kill-points mission (you don't really need the extra sergeant)
If your local is very flyer heavy, your contemptor won't be enough to stop'em all, especially as it's the only unit in your army with an
AV and will get all the love from your opponents' heavy weapons, you could benefit more from Flakk Devastators (though they are very fragile to Helldrakes ...)
You could remedy to that with a Storm Eagle with lascannons that could double as your "flying Spartan", or maybe a Caestus to put 2*5-man Termie squads in there (can't shoot at flyers though, maybe ram'em, can't remember right now), or maybe bring a friendly Thunderbolt from your Navy pals, that's one real air superiority fighter at 180 pts (and gorgeous as well)
I think you're better off with Belial than Azrael as you currently have no decent unit to put Azrael in and you couldn't take the
DW Command Squad with the banner that goes along pretty well with your total of 21 Termies
I'd take the
DW Champion in the command squad, you gotta love that S6 AP2 halberd ... (goes well with the
PC for hunting your opponent's Sv2+ as well)
(note that I tried not to touch to most of your army here, keeping it mostly intact)