Firstly, ignore adv/dis. It will do exactly the same to element as it will to crit. x0 adv/dis is around 1,500 I believe. Pig also doesn't matter.
5 phantom over 100 shots would be 5*10*100, so 5000. 8 crits over 100 shots would be 8*1500, so 12000. Or 8*1500*0.3 in PvP, so 3600.
There is more to this however, with overkilling mobs "wasting" crits, and if the extra 50 damage means you need 1 less explosion etc. However the added benefit of the burst damage crit is you can outdamage potting speed in PvP. ie, if the person can pot through your 1550 damage pet, they won't die to you ever as they can sustain that damage. But if once every ~12 explosions you suddenly do 1950, they might not be able to sustain that extra 500 damage and can actually die. If you've played WoW, PvP specs tend to be burst specs while raid specs are normally sustained damage ones (until stats get so high the burst specs kill the boss before the sustained ones catch up! Arcane mages in WoD). ie player 1 heals for 50hp/sec, if player 2 can only do 40hp/sec they never win, however if they sometimes do crits and therefore jump up to 80hp/sec for a few secs, they can win depending on player 1s hp, and how often player 2 crits.
Basically, it's a different playstyle. I prefer crits, but there is merit for element too. Many players like the consistency of elements. They know they will do x damage at all times with no variation. Others like an element of chance.
Edit: side note, crit scales A LOT better than element (element doesn't scale, its always 10-10). If your pet is instead doing 2000 damage an explosion, crit is adding 8*2000, so 16000 vs 5000 of the 5 element. The higher your base element is, the more value crit is. I seriously hope this post doesn't make crit items skyrocket in price haha.
