Don't split. Give people the choice to focus.
People like to different roles.
A game where a class are flexible, you may suffer that like to play in a not-usually way.
The reason for this is communication, as many has stated above.
If you join a group and people thinks that you should play in one way and you play in another way there is friction.
To make communication easier I think advanced classes is a good choice.
My suggestion for is that you use the same system that is use in D&D for School specialization.
The basic principle is this you have the option to voluntarily give up your access some types of magic, and then get bigger strength in another part.
I think Conjurer should have 4 advanced classes that gives it flavor.
- One that focus on direct damage from distance
- One that focus on controlling the enemies.
- One that focus on summoning.
- One that focus on healing.
And that it should exist one generalist.
By choosing the advance class that is focus on (direct) damage you gain a bonus on all you (direct) damage spells at the expense of not being able to
use any healing or Crowd control spells.
By choosing the advance class that is focus on controlling the enemies you gain a bonus on all you Crowd control at the expense of not being able to
use any healing or Damage spells spells.
By choosing the advance class that is focus on summoning you gain a bonus on all you summoning at the expense of not being able to use any healing or
Damage spells spells.
By choosing the advance class that is focus on healing you gain a bonus on all you healing at the expense of not being able to use any summoning or
Damage spells spells.
You would then have 5 advanced classes for Conjurer
Elementalist - focus on elemental damage
Green Mage - focus on controlling the enemies
Summoner - focus on summoning .
White Mage - focus on healing
Scholar - "the generalist"