Plus, the Destroyer tends to deal his damage with a relatively small number of hits, and a lot of that damage is overkill. For example, if you've goofed around with the demo, you may notice that weapons are listed as having both a DPS rating and a damage range listed. Many Destroyer skills (like the aforementioned Slash Attack) determine damage by using a percentage of your DPS total for all equipped weapons, and then the attack is treated as essentially one hit. So even my lowbie Destroyer who uses two weapons rated with "fastest attack speed" and low damage ranges can do some ridiculous crits when I use my abilities, since both weapons are up-to-date rares with great DPS ratings.
Meanwhile, my Alchemist is more like a machine gun so far. I underestimated Ember Bolt and how common Fast Cast is; it becomes eminently spammable and a few ranks into it actually turned it around quite nicely, since it becomes a multi-hit spell with multiple bolts rather than just two. It's deceptively strong since if the first bolt kills the others will keep going and readjust in flight to hit another target if need be. It's the same song with a slightly different arrangement with Ember Lance; it's a channeled spell that hits an area once every second, so again, lots of "small" hits really, really fast. Particularly delicious if you combine it with a lot of +knockback items and can sweep the Lance through a cluster of enemies. Same deal again if you go with a mob of pets as a summoner; quantity of hits over quality.
*FYI, there's a mod posted in the torchlight forums by one of the devs that gives access to respec potions at the cost of 3,000 coins each, if you guys are wondering how I've goofed around with builds so much already. I feel kinda lame using a mod, but on the other hand, it's my first run through the game, and I'm on Very Hard-Hardcore, so it evens out in the wash. Besides, I went back to my more tank-oriented defensive build in the end anyway.