Yeah, those are relative attributes, take a look at him with therapist to see the actual numbers, you might be surprised. A good use for him would be to burrow him away from refuge piles and actual corpse-making, having him chill in your dining room and dump your dead war animals to him. Those can't be butchered anyway if they died to enemies or old age, can't be buried even if they are assigned to dwarves, and if any war training, attribute-boosting (rune-engrave steelclad animal) or skill training is passed on to the bone golem, jackpot. One bone golem might be a pushover, 20 legendary fighter bone golems, less so.
As for warpstone: if you have Mason-Guild miners, you won't have any serious problems. If not, kiss goodbye to your miners if you mine into warpstone, or coal. Also, even if you don't have stable warpstone on your map, you can request it from human and dwarf caravans, and you need only one boulder to summon a tame FB from the Warpstone Pool, totally worth it. Harder mining also introduces some kind of metal wraiths and balrogs found when mining, but they are either rare or I am extremely lucky. A word on warpstone landmines though: they have a surprisingly large blast area, and they kill practically any dwarf the cloud hits in minutes. Walls and bridges and probably doors stop the effect, twists in tunnels not so much.