My road to the defiler
The defiler is notoriously one of the worst solo leveling classes in EQ2, to the point where the standard advice is to start as or betray to its good-aligned counterpart, the mystic, and switch back at the level cap. I'd actually considered a Mystic when I was trialing melee-spec priests back in the day, but I went with the Warden instead in large part because the Mystic's wolf is a ghost wolf, and I'm not that impressed with its appearance.
In the interim, I've tried half a dozen of EQ2's caster subclasses (the fury druid, and all but the coercer amongst the mages) but none of them have really stuck with me. If you've played a WoW mage, "root+nuke" simply feels inferior to "nuke and incidentally root as a bonus effect". I was interested in field testing either a defiler or a templar (which also has a reputation for poor DPS) because these two healer classes rely on spells for DPS but do not have traditional root/kiting tools. The defiler gets a nice looking black wolf and a giant spear, and is available to evil races at creation (I've been avoiding Tolkien races, I already have a Fae, and the Froglok hopping animation looks atrocious with runspeed enhancements), so Defiler it was.
Woes of a low level priest
As advertised, the DPS is pretty bad at the low levels. In particular, all priests really suffer for DPS in the thankfully-brief level 6-10 range, because their spell lists focus on healing at a time when most characters are going to be trying to get by on solo DPS. (The game's next patch will supposedly add another attack for all healers in this level range to try and improve this situation.) Your damage spells consist of a DOT and a nuke, each of which has a cooldown. If you aren't aware that casters can autoattack in between spellcasts without losing casting time or that you can combo those two spells together with the poorly described "heroic opportunity" for a bit of additional damage, you might actually find yourself failing to kill under-conned mobs. (This was my experience on my very first day in EQ2.)
Fortunately, the pampered Narache is not my first character. I had Samarya, who is going to be a Woodworker, craft the new guy some pikes. Lyriana produced some jewelry, a mastercrafted ranged slot item, and all of the spells (including a few key mastercrafts) for the trek to 20. I was aiming Narache himself at the Armorer profession, so I powered him through the crafting tutorial and promptly crafted a full set of Defiler-appropriate chain armor. I also picked up my first AA to acquire the dog, who serves as a reasonable off-tank and DPS. Though a more DPS-oriented class would be even more impressive in that setup, suddenly DPS was no longer an issue.
Overall, I like the flavor of the Defiler as a caster class. The pet is an effective addition without requiring micromanagement or making the actual character feel like their job is to provide support for an NPC. If attacked by multiple mobs, I can make a point of attacking a different foe from the one the wolf has chosen, relying on group-wide cures or damage wards to heal us both. Maybe it won't scale well into the higher levels, especially if I'm unable or unwilling to keep twinking it out in the best gear. Then again, quest content doesn't take any huge jumps in difficulty until Kunark, and level 68 would make this far and away my most successful EQ2 alt to date.
Most of all, I think it's unfortunate that a relatively unique class, which is actually well-desired in groups besides, is hamstrung by being given low DPS in the name of "balance". Unlike the melee healers, this type of character doesn't get to just add most of its possible to DPS for free while simultaneously healing (remember, in EQ2 you can autoattack at no penalty between casting, including casting heals). I don't know who exactly wins by having the classes balanced in this way, but people who are missing out on the Defiler because of the bad solo reputation are clearly losing out.