Well...[i]in D&D...[/i]... (yeah)... the power of true illusionist, can involve mimicking the effects of almost any conjuration or evocation spell to a high degree of partial reality using extradimensional energy. Their illusion spells would likely be easier to cast, last longer, be more difficult to pierce, be more resistant to dispelling, and a prestige class could be "homebrewed" to make them resistant to the use of other spells like [i]true seeing[/i], [i]revelation[/i] and [i]illusion purge[/i]... perhaps by succeeding at an opposed caster level check.

And besides, even "illusionists" (in D&D) aren't limited to using just illusions.... and probably won't be on Garrn either.

Of course, I offer only the D&D perspective here.