The Shadow
Hero
If you can already have a dwarf illusionist, what is purpose of dwarf-like gnomes?
You can have a dwarf illusionist, yes. But most worlds are not going to have an entire dwarven culture built around illusion.
I'm quite fond of the 1e Unearthed Arcana gnome. Light-hearted tricksters with good hearts. I played a couple of these back in the day, and they were tremendous fun! One was a cleric/illusionist, the other a thief/illusionist.