Sooo much subjective info here with no hard and fast evidence. I've tuned down most of my pets now, most have 10 MR and 370 Int and 2-300 mana, all are very comparible to those with max MR, max Int and huge mana pools. Very rarely do any of my pets stop for more than 5 seconds from using an ability.
From my experience even flame breath has not hindered my pets from using their regular abilities. It even appears that Flame breath (and this is subjective) has an internal cooldown. Never have I seen a pet spam it but a pet with AI and Flame Breath will cast AI waaaay more often than Flame Breath.
100% damage pets are awesome for some encounters, 100% energy against Zipactriotl/Putrifier, 100% Cold drake against Virtuebane. These are no brainers in my opinion and there are many more. FIre in general is a weakness of most of the Khaldun Spawn (Skelementals being an odd ball).
The 100% drakes have a place in the world, you just need to find it!
On PS, I find the jump from 100-120 trivial, nice to have but not essential. A major exception to the rule would be Disco as that has a direct effect on what your pet can and can not Discord.
Maybe it's because this was an older thread, but there is lots of evidence out there on the items you mention if you search for them.
Mana Regen / Mana Pool
It's widely agreed by most tamers that Mana Regen is superior to a large mana pool. Where you set your initial mana pool is personal choice or based on your pet's intensity, but most settle for around 300-500 probably. You can review our Pet Mana Regen Calculator if you are interested in the actual regen rates of different specs:
Pet Mana Regen Calculator | uo-cah.com
Casted Ability Frequency
This will depend on what your pet has and what those abilities cost. A Bushido pet, for example, will typically never run out of mana since those abilities cost so little. A Chiv/AI pet will typically dump their mana pretty fast. At that point it all depends on your pet's Mana Regen. Once they have enough mana for an ability, they will typically fire it off when possible.
Dragon Breath (Flame Breath) is a DPS loss on all pet's that have it. If you compare it to other Special Abilities and Special Moves, it is one of the few abilities where a pet will actively stop swinging in order to cast it. It also has a fairly long cast time, which typically ends up costing your pet 2-3 swings. Hopefully some day they will add in the ability for us to replace Dragon Breath.
This is also why overloading your pet with many abilities is not always a good thing, as it gives them too many choices in their ability pool and they may not always cast a desirable ability when taxed on mana.
Powerscrolls
Powerscrolls both make a huge difference and a minor difference at the same time, it depends on the scroll. Wrestling is probably the most important scroll you can give your pet, as this calculates the hit chance for your pet. You want to be able to hit as much as possible, even if those hits do less damage overall (3 hits for 100 damage is better than 1 hit for 180 damage, etc.). All things equal, 120 vs 120 is a 50% hit chance. 100 vs 120 is a 42% hit chance. 100 vs 140 and you are down to 37% hit chance.
Damage scrolls are typically the scrolls everyone thinks they
need to have, but this is where you can often find intensity (and money) when building a pet. Here are some examples of different scrolls applied:
• 24-33 Base Damage, 700 Str, 100 Tactics, 100 Anatomy:
105-144 damage per hit (pre-resist)
• 24-33 Base Damage, 700 Str, 110 Tactics, 110 Anatomy:
108-148 damage per hit (pre-resist)
• 24-33 Base Damage, 700 STr, 120 Tactics, 120 Anatomy:
110-152 damage per hit (pre-resist)
If money is tight, going with 110 tactics and 110 anatomy yields middle of the road damage and can save you a boatload of gold (and a good chunk of intensity).
You also have to consider your pet's spec and any damage modifiers they get from it (like Chiv), as they are applied on top of your pet's base damage.
Magic abilities should almost always be scrolled to 120 if possible. This is essentially your pet's specialization, and often has a huge effect on the spell damage, spell availability, and damage modifiers (depending on magic school selected).
If you are interested, you can play around with damage numbers with our calculator:
Pet Damage Calculator | uo-cah.com
We are strong advocates of taking the right pet to the right encounter and not just taking the same pet to everything. We know not everyone can specialize a pet for every encounter, but you can be a lot more effective at a lot of content with just a few different pets. Even if you can't afford to scroll them right away, save the intensity and scroll them as you get them.