Concussed is a status effect , that is not constant or guaranteed every cast
Nirn is a constant damage boost every cast
Nirn wins.
Your ' Almost guaranteed concussed ' is about 65%
20% weapon chant x 225% (?) at gold level
Charged is an awful trait on 1h weapons.
What second enchant did you plan to use on the infused offhand though?
Generally I would go nirn mainhand with weapon damage enchant and infused offhand with shock enchant for dual wield.
You can also use disease enchant (probably best option on CP campaign) since it will do abit higher damage (scaling from weapon penetration and crit, where the shock glyph scales from spell penetration and crit). But since diseased status effect was nerfed to 4 second duration down from 8 seconds, and with the increase in argonian population, I wouldn't recommend this anymore.
Also one thing to keep in mind when comparing status effects to straight damage modifiers: They don't work on shielded targets.