1. Does the damage type of armor pierce match whatever damage type the pet does? Or does it always do physical damage?
2. For my tamer that has Discord, I've made most of my pets with AI/Chiv. Wondering if that was a mistake and if I should have used AP/Chiv since my tamer dishes out discord at anything that moves, lower resists=more damage for AP.
3. Wondering if anyone has calculated a "break even" point between AP and AI based on the resists of the mob, if that's even possible with all the variables.
The idea behind giving a pet AP is to provide support for additional methods of damage other than the pet (although it will help the pet as well). The debuff provides a 10% increase to all non-direct damage the target receives.
AI vs AP on a single pet, AI will always win except at very low resists (18 and lower). However the AP bonus can apply to multiple hits, whereas AI is a single hit only.
AP + Normal Hit (affected by AP) vs AI + Normal Hit -- Now AP is better up to 25 Resists
AP + 2 Normal Hits (affected by AP) vs AI + 2 Normal Hits -- Now AP is better up to 30 Resists
This is just a pet's damage, it doesn't count any benefits to the caster's outgoing damage spells/attack, or other players attacking the target.
Add in a Necromage (or any SDI Mage) that is casting on the target, and now all spell damage is amplified by 10% when AP is active as well.
Now add in other players, and even more damage is able to be amplified when AP is active.
For a dexxer, right around 50 resists is when Double Strike/Double Shot becomes more effective than AI. So if you have just a single tamer with a Discord pet, or a Disco/CB pet, or a Disco tamer with an RC pet, you can allow an entire group of people to switch from AI to DS once you debuff the target and do substantially more damage (plus the AP bonus on top as well).
So for your discord tamer, Chiv/AI is still going to give you the better result if you are hunting solo.
I consider AP to be situational, and those situations are typically when you are doing content with a group of people (doesn't have to be a large group though). Especially if the rest of the group builds around the idea of mass debuffing and high uptime on AP, for example (aka Synergy).
Some people don't want to get that complex, which is fine, for others it can be an avenue to explore.