>>96478200
To add on to this, I ran the numbers and a 5 man squad averages 2 precision melta shots (so 6 damage) before saves. A full unit of 10 with 2 multi meltas and combis on the rest will inflict 4 precision melta wounds, so accounting for an average of EW(1) on primarchs you've got a decent chance of killing them if they fail 3 out of 4 invulns.

I usually roll very hot with headhunters so I'm definitely biased but I'm looking forward to running a ten man to make primarch enjoyers suffer.