Can someone without a doubt explain how arena scoring works?

For the most part, it revolves around 4 things: BST, skills used, merges, and unit type. Higher BSTs mean higher scores, 5* exclusive and higher SP costing skills run your arena score higher, merges greatly impact scoring, as a higher merge count, even just a couple per unit, seems to take units in the 690-700 range and put them in the 710-720 range, and unit type seems to only negatively impact horse units, positively impact armor units, and maybe slightly decrease flier types and leave infantry relatively untouched. My recommendation: do something different with Genny. She is KILLING your arena score. Run a different unit, or bolster her skill set so she helps your scores. Either that, or start merging your units to build their merge and BST values to offset her deadweight value to your Arena score.

For your skill sets, upgrading your seals fully will help your scoring standards by a great deal. Also, running a higher value C skill like a ploy or smoke skill could boost your scores since they are higher in SP cost. I would change out Genny’s hone speed though if you do keep her for a debuffer like attack smoke since she can run a dazzling wrathful build and get free debuffs and deal decent damage with it, plus it runs a higher value than hone speed.

EDIT: recommended build for Genny to optimize her ability to not hinder your score (and make her a pretty useful unit):
Dazzling Slow+
Any healing+ skill
Heavenly light
distant def 3 (for max SP and mage tanking)
Wrath staff 3
ploy skill
Atk smoke 3 seal

honestly if you want to hit 710+ i would finish that genny (also i would get panic ploy 3 seal on fae)
and looking at this that tiki is Extremely underwhelming if i were you i would replace her (summoner support included) for someone that has good speed, as well as using heavy blade effectively like ayra, mia, soleil, or even joshua (they have similar BST so they will yeild similar points) but if you don't want to or if you dont have them battle ready its understandable

one more note if you decide to keep tiki: GET RID OF HEAVY BLADE!!
with only 51 attack and absolutely no attack buffs there is no way you will even have a chance to use it
I understand it might be for arena points but you shouldn't handicap yourself over a few points, you would be way better off putting something like close Def (also why you are at it put attack smoke on genny because with her dazzling staff she can do damage and debuff your opponents for free)

other than that i would maybe swap threaten attack and threaten res for hone attack on both of them (Or you could run hone attack on genny but i would suggest a ploy)
either way, I hope I helped :)

Can add Aether to boost this team up a lot. Upgrade your seals to 3 as well.