Heavens, no! The last thing we need is a system like AC, which I would call anything but good! What we need is a return to rationality instead of delving deeper into pure madness!
1. Lower the saves of NPCs in MD+ content. They are far too high, and in Lamordia they are absolutely insane! Lower them.
• Don't repeat the mistake you made with the epification of Necro 4 more than a decade ago. Back then, DCs were also absurdly high, and DC casters were dying. Turbine solution was to introduce items that jumped from +7 to +11 stats and, on top of that, normalize the introduction of Insightful stats. No! It was a mistake that led to uncontrolled stat inflation for years and ultimately to stat squish. Do the right thing: Lower the stats of NPCs that are too high!
• All this talk about standardizing everything, and yet new content still has much higher stats than old content. Stop making saving throws and damage hits harder and harder in new content versus old! Even in heroics, there's a noticeable difference in difficulty between new and old content of the same level.
2. Skill-based saving throws are absurd and break the DC system. Skills are for skill tests, no for spell checks! Using Intimidate to draw aggro—correct. Using Intimidate on an instantkill that's equivalent to and better than a level 9 spell—wrong! The skill-based spells of the Arcane Trickster: wrong! *It's not balanced*
2. And related to the above: we should all play by the same rules. How do you expect to balance anything, devs, when you have classes playing with skill-based DCs (50 points or more difference compared to the caster DC system!), with tactics-based DCs (much easier to obtain and equip, although the final result isn't that drastically different!), and with the traditional spell DC system? Devs: it's impossible! We should all play by the same rules! We should all be able to achieve a very similar final DC score and require a similar investment effort!
* I remind you, devs, that tactics had a different system because initially they were dedicated to tests that weren't based on saving throws. But you've progressively changed all, or almost all, tactics to conventional saving throws. One has to question the rationale of this system. If they're going to be conventional saving throws, shouldn't the tactics DC acquisition system be unified with that of spells? If they're not going to be, create a rational mechanic for martial tactics instead to default to saving throws!
It can't be that caster feats give +1 to spell DC while martial feats give +4/+6. It can't be that caster enhancements give a paltry +1 to certain schools while martial enhancements give +3 or more. It can't be that caster items give +5 and have a million channels while tactical items give +12 and have far fewer channels. If it's all ultimately versus a saving throw, then the DC acquisition system should be similar.
* Regarding skill-based DCs for spells, there's nothing more to say: they're absurd and a mistake. The system isn't prepared for this discrepancy.
4. The gear for casters is absurd. I'm sorry, but it's in a fatal state. If anything needs a major overhaul, it's itemization, not the DC system. Stop separating spell DCs into a thousand channels. Merge them and make it more compact, like melee tactics. Stop making some channels absurdly difficult to obtain. Stop dividing so much by schools; there's not room for everything. And the same goes for damage: too many channels for spell damage, too much division by elements. Stop making us invest all our filigrees in spell DCs; create sets that simultaneously boost both DCs and spell damage. Stop the madness.
5. Casters and hybrids shouldn't have to sacrifice absolutely everything to achieve a functional DC. Balance NPC saves with the character DCs to achieve a rational system. The DC gained from equipment and feats should be rational: it should require effort, but it shouldn't be borderline impossible, requiring you to invest absolutely everything in it. Casters and hybrids also need to invest in damage and defenses. It can't be that DCs require such a huge investment. It's disproportionate. It's unfair. It's a discrepancy that is unbalancing these classes/builds.
As someone who has played countless casters, both first-life (including hardcore without tomes) and completionist, I have no problem with DCs on a first-life caster with appropriate gear on heroics (and appropriate gear is easy to obtain in heroics, even under hardcore conditions; it doesn't require insane gear). In epics there aren't major issues either, although having filigrees starts to matter a lot here. But then legendaries arrive, the combination of brutal saves inflation on NPCs and the absolute insane gearing makes characters with low past lives & reaper points, or even characters with PLs and Reaper Points but unoptimized gear, useless. Stop, devs. The problem with spell DCs doesn't lie on the system, the problem lies at legendary levels, and a major culprit is itemization. Itemization for spell DC is currently very bad. Really, really bad.
Spell damage has too a similar bad itemization problem.
