Channeling and Evocation allow you to create FOCUS items, for your casting ability. A Fire Channeler can not create a Water Focus item. And Why would he want to, he has no use for it.
Ritual(Crafting) allows you to create basically any kind of Enchanted item, any Kind of Potion, and Focus items to aid you in crafting. But you have no casting ability at all.
Ritual(Prefixmancy) allows you to create Potions and Enchanted items that follow the prefixmancy. And Focus items that help with your preficmancy.
So no Flight Potion for the Pyromancer, or Fire-shooting gloves for the Aquamancer. and so on...
I think you catch my meaning.
Now, I understand that by sacrificing 1 point of power when crafting an enchanted item a crafter can make it usable by anyone. Does this override the "must be in keeping with" rule, so that a Wizard-level crafter can make an armor trench coat(using Spirit) for the Fire channeler, and the Fire channeler can use it? And is the only way for a focused practitioner to have enchanted items outside of their specialty for them to have a Wizard friend?
Sacrificing 1 shift of power makes the Item usable by anyone, even people without their own slots. Yet the crafter still pays the slots.
What you are proposing is what is called
adopting items. which is absolutely legal and does not even require the sacrifice of slots. Wardens swords are the prime example, made by Luccio, carried by wardens, and each one only usable by it's "adoptive-parent".
For that purpose, the crafter creates the item with his own slots, and then gives it away to someone who has his own slots. The new owner then pays for it with his slots, at which point the creators slots are freed again.
Just be careful, because it can easily lead to the "My friend the Crafter NPC" who makes all the items... and that's somewhat lame imho.