sanguinary priest (goes with the bikers and is my warlord, always rolling on strategic)
The veritas vitae (2 traits)
He can only take a Grav Pistol, as he lacks access to the Special Weapons List.
5x devastator Squad (Primary Anti air defence and/or power armor/swarm killers)
4x missle launcher
4x flak upgrade
Since you seem to be facing more FMCs than fliers with an AV this is cool (albeit expensive), just don't expect them to do a whole lot against AV12. I'd almost be tempted to ignore fliers entirely since your meta is as it is, and use the points for Flakk elsewhere. Your army could use a squad of Lascannons, which at AP2 can much more reliably blow transports or pesky heavy support options compared to the Missile Launchers. Flakk Missiles have been OK for me in my Imperial Fist army but that's only because of their Chapter Tactics, which BA sorely lack.
As far as dropping the packs on the DC, forget that move. Just start them on-table and use their packs and run up behind cover of Drop Pods.
5x assault squad (Tank and/or MC killers)
1x combi melta
These two squads together might kill one MC, but more likely won't considering they typically have multiple wounds and invulnerable saves. Against armour they're tits though.
5 man scout (midrange objective babysitter and if the stealth traits comes up abuse 2+ cover save in ruins)
Missile launcher (secondary Anti air defence and/or power armor/swarm killers)
With Scouts missing half the time Flakk is a lot of points to use here. I personally only play mine as Snipers due to how little having a ML in the squad has done.
10x tactical squad. (midrange 2+ AS and/or medium tank killers) (the TAC droppod unit can also be fitted to be a redundant Flamer unit)
I would definitely kit these guys with flame weapons, you've already got two pods full of melta.
Overall I would swap the Devastators over to Lascannons and swap the second 10 man Tactical squad to being flame weapons as well, and drop the MLs from the Scouts and Power Swords from the DC for another 5 man Assault squad with Meltas in a Drop Pod. Depending on what way you go with it you could have enough points for a second Power Fist in the Death Company. Lets face it: 40 attacks from the 8 DC members on the charge with re-rolls everywhere are bound to make anything sweat, but Power Fists keep you relevant against things with AVs like Walkers.
It would look something like this (note that I haven't added any points up):
Priest - Bike, VV, GP
10x DC - JPs, PF
2x 10 man Tactical squads - HF, F, DP each
2x 5 man Tactical squads - LC each
2x 5 man Scout squads - cloaks, rifles each
3x 5 man Assault squads - 2x MGs, combi-melta, DP each
5x man Bike squad - 2x GG, GP
5x man Devastator squad - 4x LCs
Note that you now have too many Fast Attack choices. My way around that: Astorath and the two Scout squads are from a Combined Arms Detachment. Gives the Scouts Objective Secured instead of the +1 Initiative bonus which works, and Astorath strikes at I1 anyway due to his axe so whatever there. The only real loss is that one of your FA slots loses the Initiative bonus, which is kinda lame but not the worst. If you want to keep it to one Detachment use those point I suggested you work out (which adds up to 125 with your 20 points originally left over I think) to add in a 5 man Devastator squad with 4x MLs for some extra support.