I've never used the Druid in any MM game, for the reasons you describe. But she was pretty much the central reason for starting this game. The Warlock (Dark Druid) promo is one of, if not the, hardest in the game: firstly it's in Eeofol, which is difficult enough to get to, and then it's in the Dragon Cave, which is too tight to squeeze through with Invisibility.
You don't get the Black Potions until fully promoted, obviously, by which time you could argue the stat buffs are less useful. And you can generally find the Black Potions in the right shops, if you're willing to reload.
But I made it my central goal to get her promoted asap, and I actually enjoyed the challenge rather than another run-through with my standard min-maxed parties with all GM skills. She's definitely not as strong, but it's new as I've never played a Druid before, and there's a certain satisfaction in getting through the Eeofol Tunnels and the Dragon Cave at a much earlier stage than otherwise. If you do this, the Black Potions are actually useful at this earlier stage, and you've collected enough raw materials by this point that you can mix them all up as soon as she gets promoted, which gives you a satisfying single bump to all your characters' stats. She can dual-wield daggers and learn Armsmaster, so she's a handy enough fighter, and the Dark path game is less conducive to melee anyway. And she's also a handy backup healer, buffer and elemental school supporter. Overall, I'm glad I played her, but you do need to pick the rest of the party around her.
One final interesting thing is that when I emerged from the Eeofol Tunnels, I got the screen where Archibald appears and gives you the Blaster, along with the story about having been deposed within the Pit. I'm nowhere near that advanced in the actual game, and when I went back to the Pit, Archibald was still in Castle Gloaming as normal! The game obviously never expected people to reach Eeofol this early and the Archibald screen is hard-coded on exit from the tunnels, despite the coup being linked to your completion of his "adviser" quests