Angry Grimace
Two cannibals are eating a clown. One turns to the other and says "does something taste funny to you?"
Why doesn't the spirit have its P/T setting ability?
It's a Characteristic Defining Ability (Layer 7A) that applies before the P/T setting effect of Soul Separator, which makes it into a 1/1 (Layer 7B).
If Tarmogoyf was an 0/1 that had an ability that said "Tarmogoyf gets +1/+1 for each card type in all graveyards," it would work the way you are expecting because that effect applies in Layer 7C.