Hmm. I think the comparison is, LKali has more sustained damage. At any given point, you're likely to have the combos available to trigger x36. The total orb power might not give you much Light attack, but you have so much doubledonger power and board conversions that you can get by.
Contrast with Sakuya, who needs to drop an active to hit x36. Sure, six orb enhances between 2x Sakuya+Valk means that everyone passively gets a TPA, but the shortest and most popular active skill is still Valk at 5 turns. Granted, this means that Sakuya's x36 turns will usually be very powerful.
Also of note is that the Light orbs generated by heartbreakers
will not be enhanced unless you do so yourself. Athena is low enough on cd; LZL has healing attached that you make up for the hearts you just broke. Takeminakata adds a lot of bulk; Hera-Sowilo has a damage reduction to boot!
The last trump card that Sakuya has is that so many orb enhances will shine when your board is saturated with light orbs.
If given the chance to set up, Sakuya is a world destroying monster. This doesn't happen very frequently unless you have an Apollo active, or the boss converts dark to light for you or something, though.
LKali? You have board conversions up the wazoo that ensure you're going to deal -some- damage. That's more than Sakuya can say, being very susceptible to orb trolling unless she fields her own LKali. :V
