A few people think we will have combat power equivalent to Arcanum 16+ post Dual Transcedence. I believe this is incorrect; my intuition is, as stated earlier:
1. Arcanum Levels are like Wizard Levels in D&D
2. Eldritch Levels, at baseline, are like Super D&D Barbarian Levels (souped up because it has additional class features like shapeshifting, powerful regeneration, a secondary mind and weapon / armor formation)
3. Taking Arcanum 7 / Eldritch 7 is like becoming a strong Wizard with a Gestalt in Super Barbarian. A Level 15 Gestalt Wizard / Super Barbarian will not be remotely as powerful as a Level 30 Wizard, but will still be much stronger and more useful than a Level 15 Wizard alone.
4. While we have confirmation from Birdsie that Hermes (for combat) and Arcane Focus (for the Devoted subjects) stack directly with Arcanum for their respective domains, we don't have any such confirmation for other Aspects.
What does Eldritch do? It's basically a Klyntar symbiote from Marvel in terms of capabilities - As Birdsie said in Discord, Eldritch 4 is "We are
Venom Denim." I do believe its pound-for-pound power level in combat is higher than Arcanum, but this does not mean it
stacks with Arcanum in combat; at best it would replace our casting action with a symbiote carnage action, but it is extremely unlikely that Eldritch will scale so rapidly that 7 levels in Eldritch equals 14 in Arcanum for combat purposes. It is not as narrow as Hermes the Destroyer which grants only offense and defense; Eldritch also offers disguise, shapeshifting, mass/limb creation, second mind, regeneration and so on.
We can probably conclude that Eldritch 7 is overall superior to Seraph 7 in direct combat since Seraph 7 grants spellcasting and physical buffs, and spellcasting is broader than the ability array detailed above.
But, because we do have direct Aspect stacking in the form of Hermes + Arcanum (+ Arcane Focus), our best line for combat efficacy is almost certainly still going to be Hermes the Destroyer stacking with Arcanum. That gets us to Arcanum 7 + Carnage 1 + Hermes the Destroyer 6 (3 x 2) = Arcanum 14 combat, which is probably the realistic limit of Sol's combat power here. What Eldritch grants us is:
1. The additional +1 Arcanum. This is, by itself, worth the XP of buying Eldritch 7 due to exponential costs.
2. Passive extremely powerful regeneration, so we don't have to spend mana on defense nearly as much
3. The utility effects mentioned above, which
don't cost mana
4. A fallback combat ability at maybe the Arcanum ~8 or 9 level, which also doesn't cost mana (hitting things with the Symbiote's STATS)
5. The potential to act at double speed in concert with the symbiote
6. Free 'Will' in desperate combats as the symbiote takes control and fights at 100% of its capacity without requiring effort from Sol
7. Most importantly, the power of memes.
Unless we find a physical combat Aspect that stacks with Eldritch in the same manner that Hermes stacks with Arcanum, Eldritch alone will not offer superior results to the Hermes + Arcanum combo, though it will contribute to that combo by massively amplifying our mana and granting an additional Arcanum level.
@Birdsie please let me know if I have any major misconceptions here.