Critique my Leon build?

Imo, you are mixing offensive and defensive here (lets say im guilt of this too, since my Lissa has DC and both bold Fighter and QR3), on the one hand you have skills like LnD and SB, clearly offensive, and on the other, Deflect Missile and def refined...

I would go for one or another. So either change refinement for spd and add spd seal (53 atk and 45 spd is darn good) + add desperation, or drop LnD and SB, and replace it with Fury/Steady Stance/Warding Stance (depends for what you are aiming for) and Guard + add QR seal.

Tho imo offensive build is better.

Thats what i would do with your idea, but for me personally i would build him way differently.

+res-spd
Guard Bow+ res
Swap/Repo
Bonfire/Luna
DD3
Guard
Threaten Atk
DD3/QR3

That would make him (with 2x DD3+Guard Bow)
41
46
27
30 (48)
22 (40)

Im usually always pro balancing defensive stats (my A!Tiki has 36 def and 37res, my Nowi has 31def and 32 res).

Tho, lets say offensive build and this build are two waaay different approaches.

Replace LnD with Fury. Why gives yourself some extra defense, just to shoot it?

A lot of the stuff you chose for skills contradict each other badly. Why'd you choose Ignis as a special and have defense refine and then have LnD which takes away the effectiveness of Ignis and counteracts the def refine. Also Sword Breaker is a strange choice of Breaker imo but I could see it stopping Arya's and other fast sword her is. But based on both of the other critiques a speed refine seems like it would be better for what youre going for with Moonbow or Glimmer (I'd go with Glimmer since 54 is pretty high attack). Your SS is completely useless since Leon will retaliate against any physical ranged units and the seal only activates if the enemy attacks twice in one round before you attack.