Hi Mean Streak,
Yes, I agree Act 2 is tough for mages - I went for Speed over Magic in that Act, so I was hitting a lot but not very hard. It all changed when I became a Pyro (was an Alchemist) - I then started dishing out a fair bit of hurting (nice! )
I am also now the proud wearer of the Diamond of the Tundra, so I do have piercing at last.
I gave up the Pyro career in favour of the Necro in Act 3. I am having an easier time of it now - the Necro can dish out a lot of damage with his Shades ability but you need high Speed to make this career work (which I do have) - the Pyro isn't as reliant on Speed. Think I do prefer the Pyro though (just).
Redoubt - I agree that Book 1 is tougher than Book 2, however I fell at the final hurdle on Book 2 on my first attempt. I didn't make things easy for myself by being Hexed for a large portion of the story and I don't think I got my Warrior build right (a Drake with low armour and high brawn? Didn't seem right somehow). Anyway, I found the final battles of Book 2 were becoming too frustrating and were obviously too much for my poor Warrior build so I gave up. I'll go back to that book as a Rogue on my next go, I think. I too think I prefer Book 1 to Book 2 but I think this might be down to familiarity - I could be wrong. I'm keen to go back to Book 2 after my current LoS playthrough because I missed so much of the Terral Jungle in Act 2.