Currently the only build which actually synergizes with itself is pure mage, and it synergizes SO HARD.
Um, everything halfway decent has a cooldown of at least one turn. So it has to synergize; otherwise, it would always feel like you're using your AP in a suboptimal way after you blow through your best cooldowns. This effect is felt a little anyway, but a feeling of synergy is the thing keeping it from feeling like shtuff.
The advantage of the other classes isn't synergy, it's raw power. It's about taking a relatively simple concept (attacking), making it awesome, then repeating that awesome multiple times in one turn. Synergy is overrated.
Except there is lots of redundancy in mage spells. Already used Lightning II? Then use Lightning I. Used both of those? Use Lightning Strike.
Not to mention that you can say the same of man-at-arms, too. Any turn you spend 'just attacking' is suboptimal, since you could have been flurrying, or whirlwinding.
The difference is that Mages are hugely better since they can reduce their cooldowns so that they can throw out ridiculous spells EVERY TURN, while a warrior cannot.
I really disagree that synergy is overrated. The idea of a warrior who had synergy with Earth made Fellgnome flip his shit. He wouldn't have done that if synergy was no big deal.