Aeonic Mechanics

I have a question about Aeonics that I had 1 person in-game answer, but the answer just doesn't sit well with me. So I'm seeking confirmation.

I understand that the Skillchain properties only apply to main hand (as well as the obviously stated augments). However, it seems reasonable that the STP +10 along with the TP Bonus 500 would apply main hand or sub. Does anyone know for sure? Sequence seems like it would be a nice offhand weapon (specifically, for BLU since I have an augmented Su5 sword).

stp +10 applies, TP bonus doesnt.

Anytime any weapon has a nonaugment TP Bonus on it, it only applies to that weapon and that weapon alone, so mainhand (or ranged WS) only.
Augments don't work this way, because shenanigans with SE's coding.
And any gear or accessory with it, augment or not, works for any weapon... obvs.

Store TP will work on the offhand.

But aside from the Store TP and the accuracy and attack derived from a "121" iLv skill, there's little reason to offhand an Aeonic Weapon.
I do not recommend.

First, thanks for clearing that up. Second, I'm debating whether or not to mainhand Sequence or Crocea Mors on RDM. Same idea with BLU. Aside from the Radiance, I like the mainhand attributes of Su5 swords, but still like the high-level regular attributes of the Sequence. When wearing the Malignance set, BLU gets an excess of STP mainhanding the Su5. RDM gets a fair amount as well...just a lil less on the neck.

Couple comments regarding RDM specifically:

1. Crocea path C provides many offensive traits simply not matched by ANY weapon option, in particular the ability to become a "white damage monster" via super potent enspell damage and that Sanguine Blade will not interrupt ongoing skillchains between other DDs present. This means you can add substantial DPS to the party/alliance and yet never "be in the way".

2. However, this does not mean its suitable for every situation, in the same way that a Corsair cannot survive with a Death Penalty as their only option for shooting. Sometimes, you need that big Savage Blade for physical damage, or the like. The easiest option for those times is probably a Naegling, which will produce much better numbers than mainhanding a Sequence when buffed.

-essentially, you want a choice of weapon that is better/best for physical damage to pair with the option of a Crocea. Whether that option is a Sequence, an Almace, a Murgleis, or a Naegling depends on the style of play you want to go after along with your personal desire to build.

3. Lastly, Radiance/Umbra in my opinion is incredibly overrated. If you purposely attempt to constantly aim to make those "ultimate" skillchains, you then are stuck getting the AM back up and essentially wasting a WS round every other WS. There is rarely enough extra damage to justify such a loss in SCdmg. On almost all my jobs where I use an Aeonic weapon, I'm never aiming for Radiance/Umbra. I don't mind the AM2 adding to SCdmg, but I'd rather stick with Light/Dark beefed up by that AM2 and never losing the aftermath versus making that Radiance/Umbra and losing it.

EDIT---also don't forget when comparing the amount of STP gear available to a job that RDM gets Temper II. This makes a build centered around STP vs multiattack a lot more viable on RDM than almost any other job.