Gun bluing can definitely still scratch/wear off over time. Pistols will get a certain amount of holster-wear, along corners and edges. I'm sure it'll be the same for armor.
Yep, mild steel is mild steel. You can get off-the-shelf wipe-on bluing, but it's a bit annoying. Have to prep the surface with other chemicals first, use rubber gloves, rub the bluing on, trying to keep even coats so that it doesn't show "overlaps" or darker/lighter spots; and then it can still rust. Which means stripping the bluing down to bare metal ... rinse, lather, repeat. I tried on some scrap pieces and wasn't happy with it. Not to mention, if your articulation is off and the plates rub anywhere, it'll rub the blackening off down to bare metal.
Now, done right, it looks *fantastic* to me. I haven't been too impressed with the OTS wipe-ons, the ones I've seen that come out well are done with a heat source (like Allan's).
Paint is a good option, powder-coating is even better. It's like a hardened paint shell. Common with motorcycles (gas tanks), aftermarket upgrades on vehicle brake calipers, and / or parts that take a beating that regular paint wouldn't hold up to as well. It is, of course, more expensive, and harder to find somewhere that can do it, since it is an electro-chemical process.
