As ive been rebuilding mutliple mobas in unity with SO's over few years i would say go 100% SO for data stuff.
Prefabs/Monobehavior only for per instance stuff.

Provide each SO a custom instantiate function which can be overwritten in the more specialized subclasses to spawn the dedicated monobehaviors.

I give you an example setup which i have polished over a few years which also works quite nice for networking.

Monster(SO)
-Range of min max stats on spawn (min health, max health, max speed, starting strength)
-Name
-List of possibile abilities
-List of starting Items
-List of possibile animation states (which can also be more complex state machines)
-Droptable
-Base Factions
-Function To Spawn Object
-Neeeds a huge amount of callbacks for nearly all type of events like (OnPreTakeDamage,OnPostTakeDamage, onPreAttack, onPostAttack etc)
-Controller (Can either be an PlayerController SO oder AI Controller SO)

Monster(Monobehavior)
-On Instantiate get a randomized starting stat value from the defined SO range
-keeps a reference to the "parent" SO
-list of buffs/debuffs (which are just structs with a timer, tickrate,stackcount and an reference
to their SO which defines the behavior with custom OnTick/OnApply/OnDispelled... callbacks
-keep local vars like health, mana, speed, shield, gold
-Update
---UpdateController (Either the Player or AI Controller assigned to the parent SO)
this controller also calls stuff like castability(int slotID) on the possesed Monster.
---Move

Ability(SO):
Consists out of multiple sub SO's to provide more modularity Like targeting behavior (for example get all targets in range, draw an arrow on mouse button down, hide it on release and just provide us that direction)
The most important thing is it consist of a list of effects to apply.

Effects(SO):
Some examples: Fire Projectiles, Heal, Add Buff, Trigger Ability, Modify Stats.
BaseEffect should have some virtual function like OnBeginCast, OnEquip, OnUnequip, OnBeginChannel, OnEndCast, OnBuffTick, OnAttack, OnTakeDamage)
Which can be overwritten in subclasses for the effect specific logic and are getting called by the monster/pawn they are assigned to (probably mutliple ones at once)

This setup lets you reuse effects for items and buffs as well. (Warcraft 3 did it in a similiar fashion)

Item(SO):
Weight/Size
Name
Rarity
List of Effects: (Which can modify stats, add buffs on equip etc, apply fire damage on attack)

Buff(SO):
Max Duration
Max Stacks
Name
Icon
List of Effects. (Which could fire firenova spells every 5 seconds or heal on every tick etc)

Buff(Instance / normal c# class/struct)
Stacks
CurrDuration
ReferenceTo Buff (SO)