Neither the SI nor Wonder Woman patrol at all.
That is not accurate.
In this fic, we've seen the SI patrol in South America, in Metropolis and Gotham.
He may not run a regular beat, but it's a thing he's been known to do.
Dunno if WW does so in this AU when she's not filling in for someone.
Do know you have mentioned the League patrolling Happy Harbor.
Besides, the SI's power armour is really bulky. That plate isn't. I mean, more than her swimsuit thing, but that isn't saying much.
Doesn't change the fact that she doesn't
need the protection.
Any more than Superman needs armor against most threats, or more than an anti-Kryptonite radiation screen in his belt(which he should have installed ages ago, by the way).
Or the Martian Manhunter walking around in his bare skin, only shapeshifted.
Besides, if the plate isn't bulky, how is it supposed to produce anything near the same protection as Diana's corset thing?
Last I checked, Hephaestus forged that thing, while investing magic in the thing.
Not sure how Ted Kord and OL are supposed to get anywhere near the same levels of protection in a near-equivalent package.
Your fic, your rules.
But from where I stand, it looks like your SI is basically trying to stick WW in trousers and shirt because it offends his sense of aesthetics.
Which would be an interesting exploration of his attitudes if he acknowledged that was what he was trying to do.