This is not accurate. Each caster has different mechanics, much more than what D&D provides.
Bard: 2 cantrips known, 3 spells known, 3mp, Bardic Performance (1mp 1ap, provide bonus) Font of Inspiration (Help better) Remarkable Repertoire (normalize spells known)
Cleric: 3 cantrips known, 4 spells known, 3mp, Order (Damage type manipulation plus heavy armor and weapons, advantage to knowledge, or extra HP on heals) Blessing (1mp 1ap, heal/help/harm) Divine Omen (1/Long rest Augury)
Druid: 3 cantrips known, 4 spells known, 3mp, Domain (1mp 1ap, control/heal/move) Wild Form. (daring choice, homogenizing wild shape into a generic 'beastman' type creature)
Sorcerer: 3 cantrips known, 3 spells known, 3mp, Innate Power (Slightly better magic knowledge but oopsie table) Overload Magic (Bigger Magic and Exhaust yourself) Sorcery Spell (Know an extra spell)
Warlock: 3 cantrips known, 4 spells known, 3mp, Bond (Harm, heal, advantage) Pact Boon (Armor, Weapon, or Cantrip Mastery on a single type, or have a pet with extra familiarity) Bessech Patron (Maybe patron helps, maybe not)
Wizard: 3 cantrips known, 4 spells known, 3mp, Spell School (Know one more spell and cast easier) Arcane Sigil (1mp 1ap, good spellcasting bonus)
It's SO Tedious to write out the same stuff over and over like that. I had to bold the class so I remembered which one I was on.
Anyway: All of them follow the exact same casting mechanics, which is what gave Warlock a significant difference both at it's time of creation in 3e and it's 5e version. Homogenizing them badly.
Similarly, everyone knows the same amount of spells and cantrips and has the same MP progression across the first 10 levels so they can cast exactly the same quantity of spells and/or empower the exact same amount of cantrips/spells through "Mana Point Enhancements"
Which, of course, adds some spellcasting flexibility, but is going to utterly gut any variety of concept if and when the Dungeon Coach decides to put his Psion into DC20. But at least his "Commander" made it, in an attempt to make this book as 4e as possible.
And what imbalance? That statement is not the reality of how playtests have gone. You're also completely ignoring how there is more development to come, and this game actually cares deeply about both balance and flavor, and has the capability to constantly refine itself and directly include our feedback, unlike current D&D.
Druids get their "Full HP Combat Form" setup like 5e which basically grants them an extra "Health Bar" since they can swap into it at any point, 5e style. It has never been a balanced design.
Similarly, Cleric and Bard are pretty similar except the Cleric can suddenly wield heavy armor/weapons/shields for no apparent reason. Or be better at casting spells. Or have constant advantage on knowledge checks and an extra knowledge skill known. But hey, the Bard gets 2 skills known so at least it's not entirely in the Cleric's favor.
1ap/1mp appears a lot because it's the "Balancing Metric" but the functionality of it wildly varies from granting the ability to do things you otherwise couldn't for free (Druid) to expending the rest of your remaining resources better (Wizard) to just applying blanket bonuses (Bard) with very different levels of value based on when you use it and how much MP you've got left. Of course then you've got the Warlock cutting themself for the same kind of bonuses trading 1hp for 1ap/1mp to give you an idea of just how valuable it 'Should' be...
As far as "Refine itself directly" that's just what playtesting -is-. The playtesters who were part of the 5e Alpha back in 2012 or 2013 also got to help "Refine it directly". Just like the playtesters of the Voidrunner's Codex by ENPublishing got to do several months ago. I know. I was one of them.
Meanwhile for A5e I don't just "Refine" material other people created, I signed up for the Gatepass Gazette submissions E-mail and provided new material for the game. Which is now part of the official rules and accessible on A5e.tools or as part of a pair of beautiful GPG Annual hardback books.
None of which touches on my previous attempts to move the Dungeon Coach away from underpowered design for new material.
Though hey. Maybe once the playtesting is done and the feedback is exhausted, things will be in perfect balance! And then he can create another splatbook to add a class that is woefully underpowered and employ playtesters, again, to bring it up to speed.
But that's not a design philosophy I stand by.