Summoning most things are useless unless you can get at least 2 of them off a turn at which point you are spending a fair amount of points, T3 5++ its really easy to kill, and a herald cannot join a unit until the next turn so in most cases will just die. Granted it takes the firepower away from something else but certainly in smaller you aren't going to get that much. Bloodcrushers may be useful T4 W4 and you get three of them so ho know with that but most things aren't going to last, especially with the ridiculous amount of dice you will need to do it.
Pretty sure Bloodcrushers only have three wounds each.
But yes - as our games today proved, using Malefic to summon a bunch of Daemons doesn't really work with 2 Mastery 3 Sorcerors (even with one with Prophet of the Voices to avoid Perils) as you simply can't push through enough casts to get a horde of Daemons. They just end up being easy combat victories (and therefore easy extra movement) for your opponent.