Stats, gotcha.
Skullcap and Circlet sound like a fine place for flavor. The only trade-off apparent to me is Garnet would boost Leviathan in slightly less defensible gear: a very minor concern.
Re-adding missable synth materials sounds good.
I ran some numbers on the scratchpad on the mod's main spreadsheet to see what sort of damage the (Str+Mag)/2 formula weapons might do at max stats. These are averages of min and max damage.
Tiger Racket: 1837
Angel Flute: 3220
Whale Whisker: 3667
Whale Whisker (old): 1976
Mace of Zeus: 3504
Sargantas: 3300 (selected because as comparable w the above)
Obelisk: 3827 (selected because as comparable w the above)
Masamune: 5025
Ultima Weapon: 6000
Ultima Weapon (old): 6750
E2: 6300
E2 (old): 7350
Basically, if considering max stats, you can pretend that Garnet and Vivi wielding a Str+Mag weapon are wielding a Str weapon w the same power and a Str of 72. Eiko, 71. Whereas if they are wielding a racket/Str+Spd weapon, they do so like they are wielding Str weapons of the same power with Str of G: 43, E: 42.
Since row doesn't matter for striking your own party members, Healer on mages is much improved.
Edit: Would you say the main value of the rebalanced attack values is so that the attack values themselves make more sense internally?
Did you go ahead and change daggers to the (Str+Spd)/2 formula like you mentioned?
I can be available to discord chat some time soon. I don't use Discord much, so I'll figure it out after work today and plan to reply more about it to your next replies.