Just a messy post to dump some of my ideas into;
“Dipping” into skill lines is easy to get access to a few specific abilities. This is most obvious with abilities like Cloak and Dagger, Tactical Retreat and similar. While I like and understand that you can dabble into skills to access their abilities without mastering them, the way the game is balanced does not reward this due to the way abilities scale. Main attributes giving raw damage(and thus forcing you to pick one for optimal efficiency), and the multiplicative scaling of the skill bonuses are a big part of this.
What if neither strength, finesse, or intelligence increased the damage of your abilities directly, but instead have an effect that is effective for everyone, but some getting a greater benefit than others, for example; Finesse giving Crit damage % would benefit dagger users most, but still benefits others.
On that note, I think crititical % chance should be innately built into weapons(and spells*) themselves as it is already for daggers. Maces having a low(5%) chance, with swords having a higher(30%) chance, with their baseline damage being adjusted to compensate. Daggers staying as they are, with their effecive 100% chance when behind a target, and X% when not.
Right now critical hits are to prevalent late-game and nearly non-existent in the early game. Removing the chance to land a critical hit from everything but base weapons depending on type and talents like Savage Sortilege would help a lot to this end, I think.
*(Savage sortilege also giving a 10-20% chance to crit alongside allowing spells to crit that can otherwise not crit.)
Attributes should have secondary benefits as well; Strength has the carrying capacity and opening/moving heavy equipment. This is good, but similar benefits should be given to the other attributes. Finesse to help with tasks that require fine finger-movement, like thievery. Which brings me to something else really quickly;
Civic talents. Pet Pal is a really cool talent, but it does not benefit you in combat. Instead, a new slew of civic talents which help enable content; Pet Pal, Thievery, and Telekinesis would all be talents. Pet Pal is influenced by a variety of attributes depending on the conversation, Thievery would rely on Finesse how effective it is, and Telekinesis on intelligence. (On that note; telekinesis needs to be more widely applicable and have more puzzles/shortcuts that would warrant its use)
It might be best if all civic skills are either moved to talents, or made baseline and influenced by attributes. (or a combination of the two) At least, if there aren't enough civic skills left.
Now back to regular skills; If they no longer scale by main attribute, what stops people from making weird combinations? Well, nothing, but neither does the current system which merely makes them subpar. But the current system also effectively stops you from playing actually interesting builds like a battlemage.
With main attributes no longer boosting specific weapons or skills, more options for players open up. The damage bonuses of skills and the physical/magical armour system as they are remain an obstacle to hybrid characters and the latter for parties.
First, the damage bonuses of skill investment; They're a multiplicative increase which exponentionally grows the gap between hybrid and “pure” characters(pure being defined as; all skills synergize towards benefitting a single goal; dealing damage with a bow for example)
Making them additive does not actually solve the problem(and meaningless if main attributes give no damage increase), as it merely makes the difference grow at a slower rate compared to someone taking points in Pyrokinetic and Geomancer(whose benefits do not apply to the other). Instead, I would like to see the benefit you get from skills to be defensive in nature; Pyrokinetic giving fire resistance, scoundrel giving dodge % etc.
This would make each attribute give something flavorful that is of value, and can be a visual cue of its strong points: “He used a fire spell? Probably has quite a bit of fire resistance.” You would need to change at which skill levels you can use certain abilities to avoid just dipping into everything so you can use anything; jack of all trades, master of all is something you want to avoid. To that end, I suggest increasing the level you need in a skill for nearly all abilities. Power * Archetype fantasy, reduced by how weird it may or may not be for another character to use an ability like that. Uncanny Evasion, an aerotheurge ability, is quite powerful, but doesn't fulfill the archetype fantasy very strongly, it's also not weird to see a scoundrel or archer using it so this is an ability that someone who dabbles in the skill could use, so a tier 1, or skill level 1 required skill.
Other skills, like Tornado, have both a high power and archetype fantasy, and it'd also be unlikely for someone who dabbles into the aerotheurge skill to use, this is a higher tier ability at about 7 or higher. Especially movement abilities like Cloak and Dagger/Tactical Retreat/Phoenix Dive make this dipping quite bad and reduce flavor in favor of mechanical benefits. One additional suggestion regarding the movement abilities; making a special slot or two for abilities with that function, but allowing duplicate abilities(ie; you can have 2x tactical retreat, or 1x Tactical Retreat and 1x Nether Swap for example). (And make Phoenix Dive a Pyrokinetic ability, and give warfare a leap)
This way, people can play a jack of all trades, master of none and not be punished by numbers, but they won't have the mastery of the elements of spells like earthquake and tornado while also striking a mortal blow from stealth beforehand which are some of the archetype cornerstones of skills like aerotheurgy, geomancy, and scoundrels. While yes, to an extent the current system also prevents this, but it also prevents the battlemage archetype, or any other martial character which dabbles in offensive magic.
Secondly(Oof, took a while to get to the second point), the physical/magical armour system. Right now it cuts off interaction between physical and magic damage users completely. Instead; Physical armour reduces damage of physical attacks by ~30% (could be more or less), and magical armour that of magic damage by the same %, but only 50% of the reduced damage is absorbed, the rest going directly to vitality. When one armour type is gone, the remaining damage goes to the other armour type which does not reduce that damage type. This would make a mixed party still useful to pick off individual targets, without having to both hack at a separate health pool first.
Very important to note that this does require debuff protection to change because armour goes down slower; making thesholds of armour to show what kind of debuffs can be applied. For example; Chicken Claw or Frozen might require physical or magic armour to be between 0-30% or be resisted, while Bleeding or burning might require 0-80%, effects like silencing 0-50% etc. (all of the % are outlined on the abilities that apply it).
Now on to my final point for this mess; Physical damage types.
One of the problems of magic vs physical is all the resistances that magic damage has against it. One way to balance this is by splitting up physical damage into 3-4 groups;
Piercing(Arrows, daggers, spears, half of the damage from swords)
Slashing(Axes, half of the damage from swords)
Crushing(Maces)
Necrotic(decay/infestation and the like)
With enemies resisting each damage type individually, just like with magic damage. Skeletons being weak to crushing, but strong against piercing for example.
Relating to weapons; we need a weapon swap to be done easily with this change, which alongside the other changes would allow you to actually build a character that can effectively use a bow while also swinging his sword in melee.