So... here's an example structure. The Swordmage. (To be clear, I haven't designed the class, yet, this is all theorycraft)
Importantly: Cantrips do not Scale in this setup. Maybe I should call them "Orisons" or something similar.
Level 1 they get cantrips, weapon proficiencies, etc. They also get 2 spell slots and access to 1st level spells. They can prepare a number of spells equal to Proficiency+Int with a minimum of 1. At least 4-5 of those spells are attacks, another 2-3 are defensive spells, there's also some control and utility in there, as well. They'll also get their spellbook-type mechanic at level 1 to store spells. You can still upcast lower level spells into your encounter spell slots, and your spell slots always act as the highest level spell you can currently cast.
At level 2 they get some new class features. The first allows them to use cantrips to dual-wield following all the same rules of dual-wielding as previously outlined except they cannot be holding a second weapon in their off-hand. The second grants them either an exploration or a social feature, depending on which option they choose. This puts all pillars into the class, and allows a character to build for social in city games and exploration for dungeon games or split the difference as they gain levels.
At level 3 they get their archetype. The archetype provides them with a new exploration/social feature, and a new throughput option that highlights their archetype's identity. Each of these archetype-identity abilities eats a spell slot to use, maintaining the encounter paradigm. You'll also get either a movement or defensive feature from your archetype that you just get to use as an action without expending spell slots.
Level 4 is your ASI or Feat, per normal rules. You also get a Social or Encounter feature, here.
Level 5 gives every class, Swordmage included, Extra Action. There is no extra attack. There are no scaling cantrips. Attacks, spells, everything is just another action and you get two of them at level 5. That's two sword swings, two cantrips, etc. This comes with the rule that you can only expend exertion/spell slots/psi dice on a single action on your turn. So you could spend exertion on your first action to make an attack with a rider, then make a second attack without spending exertion. Or use a spell slot and a cantrip. Or make a weapon attack and use a cantrip. However you wanna do it. Bonus points: Your Gish now Gish at level 5 by being able to attack and cast spells on the same turn.
Level 6, everyone gets their dailies! Wooooo! This is something you can use 3 times per long rest, but only once per encounter. For Arcane characters this is probably, like, "Greater Arcana" or something similar for a naming convention. They'll be spells much more potent than the traditional spell slots you get to use, and cannot be used on the same turn as an Encounter power. At the highest levels, this is where you get Wish and stuff. In addition to learning a number of these equal to proficiency+Int, you'll gain another social/exploration pillar option here.
Level 7 is where Swordmages get their next archetype ability which is a pair of things. A new spell slot active ability with a constant passive benefit tied to it, and an archetype-specific social or exploration ability.
Level 8's another ASI/Feat with a 3rd pillar ability.
Level 9 gets you a new class feature that is primarily defense/control. This could be a 'sticky' feature that allows you to force enemies to reroll a save against a control effect they just succeeded as a reaction to try and keep them trapped. Or resistance to a damage type. Small list of options.
Level 10 gets you a new big feature! This is a core class identity function which provides defensive benefits to yourself and your allies without the use of spell slots. Maybe the ability to drop a "Thunderdome" like ability, temporarily trapping enemies inside with you while keeping other enemies from helping them.
Level 11 onward: Mostly more spells and uses of spell slots. Occasionally you'll get some nifty features that provide benefits to your allies, but as a swordmage most of what you do is hit things with a sword and cast spells.
Worth noting: They get access to 2nd level spells at 5th level, 3rd at 9th level, 4th at 13th level, and 5th at 17th level. These are the levels where their encounter powers just straight up become better and more powerful, independent of class features. These are also the break-points where you get access to a new spell prepared (aside from improvements to intelligence).
Social or Exploration Features: Whenever you get one of these levels, you pick from one of two lists of what are, essentially, invocations. Every class will do this, and every class will get their own lists. Though there may be some overlap options for power sources. Every Martial character, for example, might be able to take Forced March exploration features that let them replace one ally's failed Con Save with martial character's success once per hour. Every Arcane character might be able to get a Knock invocation that lets them use the spell without using a spell slot or taking the time to do a ritual, making it more useful in dungeon encounters where spell slots are limited.
