3e warlock is great model to build simple caster. It had no spells per se. It had eldricht blast ability that progressed like sneak attack with levels and few invocations that were at will "spells". Something similar could be used for basic magic user. Mana blast - basic spell attack, invocation spells - few select control/debuff/utility spells which are at will and thats it.
I must get round to writing my Warlock "Pact Transformation" spells - a collection of half a dozen to a dozen warlock spells all of which require a pact magic slot to cast and work until the spell slot is recovered (which you can choose not to do). The obvious one is
Pact of Power
1st Level Transmutation
Casting Time: 1 minute
Range: Self
Components: V, S, M (Ten drops of the warlock's blood)
Duration: Until the spell slot used to cast this is recovered. If you would normally recover the slot you may choose not to do so to keep the Pact Transformation running.
Special: A Pact Spell can only be cast using a Pact Magic spell slot or a Mystic Arcanum slot; using a Mystic Arcanum slot always counts as a pact slot of fifth level.
Special: While you have a Pact Transformation active you may not concentrate on any spells not granted by an Invocation or a Subclass. You may not have the same Pact Transformation active twice at the same time.
You are imbued with mystical power that reflects your patron, visible either in your eyes or whenever you make an attack. Whenever you make an attack you do a number of points of extra damage on that attack equal to the level of the Pact Magic slot used.
It's designed to compete with Hex (which is why there's a slightly awkwardly worded concentration restriction built in; I don't want this stacked with Hex - and I don't want to lock someone out of subclass features entirely). And I want for players to just be able to scratch out their spell slots, gain a few abilities, and be done.
Also:
Pact of Sight
1st Level Transmutation
Casting Time: 1 minute
Range: Self
Components: V, S, M (The warlock's own eyes, which have a visible supernatural effect for the duration of the spell)
Duration: Until the spell slot used to cast this is recovered. If you would normally recover the slot you may choose not to do so to keep the Pact Transformation running.
Special: A Pact Spell can only be cast using a Pact Magic spell slot or a Mystic Arcanum slot; using a Mystic Arcanum slot always counts as a pact slot of fifth level.
Special: While you have a Pact Transformation active you may not concentrate on any spells not granted by an Invocation or a Subclass. You may not have the same Pact Transformation active twice at the same time.
You are imbued with mystical sight, and your eyes reflect your patron. Unless you have concealed them everyone looking at you knows that your sight is unearthly. The exact augmentations to your sight
Level 1: Darkvision 60' (or extend your darkvision by 30' if you already have it)
Level 2: Understand the literal meaning of any written language you see
Level 3: Advantage on search and perception checks to notice hidden or concealed creatures or objects
Level 4: Permanently see the presence of magic within 30' of you, learning the school of magic. You need line of sight to the object to detect it
Level 5: Blindsight 30'
(If you want x-ray vision there's already an Invocation for that).
The point of this is to lock down what you can do so you can ignore the spell slots.