-Silencing/Interrupt mechanics have no effect at all.
-Pets are far more tankier(not to mention you don't lose that much DPS for healing them, compared to Warlocks)
-Pets have more utility(you can literally bring any debuff/buff/cc as BM)
-Deterrance trivializes a lot of encounter mechanics
-Feign Death and Camouflage for skipping trash/avoiding mechanics(Feign death drops off beam-tracking on Atramedes flight phase for example)
-Can do full rotation while moving all the time
-If it can be slowed, it can be kited endlessly(Or if the mob is slow enough, Aspect of Cheetah)
-Lots of CC, single target/AoE Slows, root, sleep, silence, stuns, disorient, psuedo-taunt
-Strong self heals through Spirit Bond(1% every 1 second pretty much and is Passive) and Spirit Mend(BM only)
-Very strong(best in game imo) instant AoE
Hunters just are kings at soloing stuff, Blood DKs only have such massive Self heals that they don't have to worry about anything at all really
Warlocks can use felhunter as an interrupt if they need one. they also get that interrupt through grimsac.
You can only use a felhunter as an interrupt if you can keep it alive, which because it and every other warlock pet (except the blue ball) is so squishy is only possible versus an interesting opponent if it doesn't have aggro, which is kind of backwards in the world of pets.
Meanwhile GoSac should never have been implemented and I hope it's removed or made a 1 minute ability or something like that.