[Baalz]

blood rain, leech, bloodletting, rush of strength, hellbind heart, summon imp (haven't really used hellfire much) and later go to hell, blood vengeance, rush of strength are all top shelf battle magic if you use them properly. Life for a life, sabbath slave/master, reinvigoration are all niche, but very useful. Several other blood combat spells are quite useful in small niches (call horror, hellpower, etc.)

How many other paths have that many good combat spells? Blood isn't used much in combat, not because of lack of good spells, but because of the pain of managing blood slaves. Heck, just look at how widely used the inferior (other than the need for blood slaves) versions of the spells I list above are:
terror/panic
strength of giants
drain life
charm (hellbind heart - much better because it's easy to spam with cheap mages)