Pets get the following boosts in epic/legendary:
+45/90% physical, elemental, vitality, poison
+30/50% pierce
+30/50% to damage over time effects
^Those do not appy to traps
They also get, in epic/legendary:
+30/60% to basically all damage types
A lvl 16 wolf does 27-49 base damage. This translates to
27*(1+0,6+0,9)*(1+(150/500))+150*0,04 = 94
49*............................................... ............= 165 damage in legendary.
If you get flat damage bonus for your pet, it is modified by the difficulty bonuses, not by str.
+x% bonuses are additive with difficulty bonuses.
Pets get the following stat boosts in epic/legendary:
~+200/400 health
~+200%/500% health
~+100%/200% mana
A bit of run- and attack speed
+350/580 OA
+350/600 DA
Pets get boosted by Art of the Hunt but not Balde Honing.
Here's a pet resistance table:
