Yeah, guardian pets are dumb even compared to standard pets afaik they will not switch targets at all unless the original one dies. Moreover, a cooldown like Dark Soul affected all damage, and could be tied with other cooldowns and procs as well.
And the temporary pets costing a shard mean certainly for affliction, they simply aren;t worth it. Just take Supremacy as a permanent fire and forget dot.
Afflcition is in a good place but Supremacy is just the go-to talent. Not least because in dungeons it's a cost-free way to swtich between more single target or more aoe, just use Doomguard or Infernal as required. The affy pet is the dog, which is a sucky melee pet with no gap closer....
If they want Service as a viable choice for aff they'd have to remove the shard cost, or bump up the damage even higher, it is simply not worth losing a potentially big-critting UA