The thing is that we all agreed to use Daemon world rules for this battle, a ruleset I never plan to play again. Most of the time the warp fell in their favour with Khorne smiting our units and Skulltaker possessing my ally's Librarian who was also acting as the Blood Angel's Warlord (see middle left picture). It was by far one of the most embarassing ways to give 2 victory points to our opponents - one for Slay the Warlord and First Blood.
I'm gonna go to the spoiler, we were almost tabled with all but the Imperial Knight being wiped off the board. The C'Tan (see bottom left picture) put up a valiant fight against the Great Unclean one, stripping all but a single wound off him before being charged by 10 Flesh Hounds and being enfeebled twice. Still, he exploded and took some of the beasts out with him. My Warriors and Immortals lasted a good while before 2 Daemon Princes and a Lord of Change massacred them all in sweeping advances. I was lucky that one of my Tesseract Labrynths caught one of the Daemon Princes. I also stripped all but 1 wound off the Great Unclean One, all but two off a Lord of Change (which was hard work!) and took 2 wounds off a second Daemon Prince.
I won't go into massive details on why we lost, only that some annoyingly good luck on our opponents side and some disgustingly bad luck on our side (my Wraiths failing to charge by 1" and being blown away in the next round of combat springs to mind) plus some very hard to kill daemons didn't help our cause, not to diminish our opponent's victory.
But the most valuable lesson I learnt was Desperate Allies hinder more than help. I found my Annihilation Barge and C'Tan Shard unable to do anything for a turn and they were crucial to my plans.
Next time Daemons, next time...