Part of the problem is the disparity between what different classes get as part of their basic package, particularly at lower levels. I would consider making it so that the class chassis are the basic versions of the class and the subclasses then are an additional layer that you can add-on, which would also increase modularity.
I would go with Vowed (see Vowed in Worlds Without Number or the Oathsworn in Arcana Evolved) to even move away from the "mystic" and ki aspects. The Vowed gets their powers from the vows that they swear, similar to Paladin oaths.
The Berserker?
I like that idea.
If I had my way, I would borrow several ideas from PF2, namely unified spell lists: i.e., Primal, Psionic, Arcane, Divine. Classes would then be designed around playstyles: e.g., no-armored scholar class; gish; war caster; innate; pact/summoner; etc. So if you wanted to be a Wizard, then you would pick the no-armored scholar class plus the Arcane spell list. But you could also be a scholar-class with the Divine spell list (i.e., Cleric) or a scholar-class with the Psionic spell list (Psion).
Choosing the subclass archetype at level 1.
Structurally, level 1 has about the same amount of information as two levels combined.
When thinking about the "base class" features and the "specialized archetype" features, I find it conducive to treat the "specialized archetype" as level zero abilities, and then add the "base class" as level 1 abilities.
Narratively, the character first demonstrates a talent and aptitude for something specific early on during "level zero" sotospeak. Then later the "base class" training helps round the character out to be an effective and versatile member of the class.
Because the specialization happens at level zero, every level 1 character includes a specialized archetype.
It is even possible for a character to specialize in something else at zero (such as casting a cantrip), but then switch to a different base class (such as Fighter). Mechanically, this is moreorless swapping a class feature, but it can help add verisimilitude to the biography of a character.
What is most salient about a Monk? That it is a martial unarmed combatant, or that it is a magical class? Maybe rename the Monk "Athlete"? Let the subclass archetype determine the magical abilities of the "Athlete", if any.
Berserkr is a reallife name, and refers to magic. Conceptually, the tradition reuses (feminine) shamanic magical techniques for the purpose of (masculine) combat. The ferocity of a Berserkr is because the mind of the Berserkr has become an animal − and sometimes the physical body transforms into that animal as well. Essentially, shapeshifting magic.
The do-anything "Arcane" power source might work better splitting up into several power sources, such as Elemental, Necromantic, and so on.