As an Enchanter, yes he is unable to cast Invo/Evo spells, i.e. the flashy mass damage one like Fireball, especially. However, he does have access to a lot of disabling spells, which are basically the same thing as a fireball - if all of your enemies are asleep, for example, then they are pretty much dead anyway, given how easy it is to dispatch them while asleep.
Dynahier, as an Evoker is denied spells from *two* schools, both Enchantment/Charm *and* Conjuration/Summoning - and any experienced player can tell you that the various versions of Monster Summoning X are *very* useful.
So no, Xan doesn't have access to Fireball etc, but he *does* have access to lot of spells Dynaheir doesn't - which balances things out, IMHO. Personally, I'd rate Sleep as a much more valuable spell than Fireball - you will be using it for longer than Fireball and as a 1st lvl spell, it is not only quick to cast but you can have a lot of them memorized [especially with the Ring of Wizardry, which *doubles* the # of 1st lvl spells you can cast per day.]
As for his personality >laffs<... yeah it takes a bit of getting used to and certainly isn't everyone's cup of tea.
Certainly, I'd recommend that people check him out and use him to best advantage, just as they should check out Dynahier, as well. As for Edwin, well... no thanks. Yes, he's a great mage, but he's no hero and has no place in my Heroic party! :) To each their own, of course.