Well, from what I've learned from my - single - playthrough, and from what I've seen on the forum here, Mages can put together some pretty decent equipment - that is, if they're willing to completely neglect armour.
An Alchemist's advantage over the other Mage careers is that they're not item-dependent; they can keep that talisman spot for something that gives an extra point in Speed.
On the downside, an Alchemist probably won't do a lot of passive damage per round, or be able to hit several enemies at once. I was very tempted to change to Pyromancer when I found the appropriate item. Ignite/Burn/Embers would have been just lovely. But in the end, I really wanted to hang onto that extra point of Speed. Plus I didn't really like the idea of being dependent on an item for my career - an Alchemist's abilities, non-focused on combat as they are, are at least 'inherent'.
On the other hand, completely neglecting Armour can prove tricky too - even with a high Speed, I found it absolutely impossible to get past King Louis, the big white ape, in Act II. His huge automatic damage per round, and me having no armour to soak it up, just made the fight too difficult.
Ah, Mathis I can take down, but the great big monkey is the one that got away...