*Holds gauntlet up, lets it drop.* ; ) I was thinking about this recently, and I've finally figured out why the Malakai Priest seems such a poor choice to me: because the (Straywood) Beastmaster does it all better. I shall explain:
Holy Avenger:
First, there's these two problems: "...the first time it attacks an enemy creature who attacked and damaged another friendly creature or Holy conjuration..." It would have been much better if this had said "whenever" instead of "the first time", and left out the "and damaged" part entirely. Most Holy creatures and conjurations have defenses, or high armour, and thus have had their life reduced when compared to other creatures in balance. But the HA needs damage to be taken to trigger its bonuses. This effect can also be manipulated by your opponent, since he can usually choose which of his creatures attack which target in what order. And finally, the current meta has only the Asyrian Cleric as a low-level creature choice for HA, which...isn't exactly ideal for the role; the only other options are 12-13 mana level-3 holy creatures. Four additional mana for a special ability that is of limited use? No thanks. The Beastmaster's Pet is soooooooooooo much the better option, it's not even funny.
Malakai's Fire:
The Priest starts with 9 Channeling. Bringing out his HA costs additional mana. And then, to add insult to injury, in order to inflict a Burn token he needs to spend a mana each time. For this ability to be worth it, ideally you want to be using it every round to keep up the heat--which effectively causes the Priest to have 8-ish Channeling. On average, a single Burn deals 3 damage. However, using it requires Light damage, which means either his 2 dice base attack (which is at least one die less than any other mage), a Staff of Asyra, or attack spells. --Which effectively means the 8-mana Staff of Asyra is required equipment, asap. For the already mana-starved 8-channeling Priest. Meanwhile, the Beastmaster doesn't have to pay a mana every time he wants to use his +1 Melee ability, and can equip the 5-mana Mage Staff and deal almost as much damage (although no Daze/Stun chance). In this case, the Priest actually comes out ahead in potential overall damage, particularly with the Dawnbreaker Ring and Daze/Stun factored in--but it's just too mana-intensive for the manaphiliac Priest to realistically expect to effectively use. (He really is just pouring out the mana.)
Creature Pool:
This issue will likely be corrected over the long term, but the fact is that currently the Priest's creature selection kind of sucks for him. The mana-starved Priest needs to have multiple creatures out so they can take damage and trigger the HA, which means those creatures hit will likely need healing (or replacements when they die). All of those creatures cost a minimum 12-13 mana, irrespective of all the other mana being drained out of the Priest by everything else he needs to do. This is a nightmare. Meanwhile, the Beastmaster's problem is which mana-efficient and effective low-costing creatures to exclude from his book, because he's got too many to be able to include them all. (In addition, the Beastmaster even has his Ring of Beasts to reduce mana issues even further.) Once again, Beastmaster wins effortlessly.
There are other examples I could mention--most of the best creature enchantments are in the Nature School, for example--but these are in my mind the biggest issues. I think the Priest suffers from a slightly lesser version of the Warlord's problem: the Wizard does (almost) everything the Warlord can do, and does it much better than the Warlord. The Beastmaster does (almost) everything the Priest can do, and does it at least slightly better than the Priest (and in some cases, does it much better).
Thoughts?