I couldn't guess on what footprint used for steel, but would guess the bulk of the chisels made in the last 75 years came from drill rod or wire rod, whatever you want to call it, snipped off, die forged and then run through a grinding process (before of after heat treatment for certain parts, depending on the process) and heat treated by something quick (not by some elaborate schedule like you'll find in bohler's listings).
What's the point? Well, if you get 1% drill rod with minimal bits of things (manganese, chromium, a little bit of vanadium, etc) added, the steel will harden well and temper around 61 hardness in the sweet spot (where the steel gets adequate toughness but before making it soft so that it won't chip at all - it just rolls instead, which is worse for chisels, anyway).
If you cut the carbon to 0.8, then the same temper will result in a point or two less, and if you cut the carbon to 0.6, then you'll get something around 56-58 hardness unless you short tempering (no good). The steels with lower carbon end up being much tougher, but they lack strength - toughness is how much energy steel will take out of a weight before it breaks, and strength (at least the first phase) is how much force it will take steel to deform. The toughness tests go way past deformation to failure, but we want to operate in the strength range unless opening paint cans (then it's probably good to be able to fold the edge without breaking a chunk off.
The cost difference between good 0.8% carbon drill rod and 1% is a small amount, but if you're going to do post heat treat grinding, any additional softness makes things easier.
We don't get much in the way of *really good* chisel steel because there's not that much of a market (there's a little niche one now) for cabinetmaking chisels vs. something that doesn't get returned when someone uses it to open a paint can.
There's literally nothing that would prevent a chinese company from using 1% or 1.1% plain steel and making really good chisels (better than the aldi chisels) for a couple of dollars each, properly ground. Except they're not aware of it and nobody is going to distribute superb chisels for $5.
The rust as far as chisels go is a good thing. Additional alloying does nothing for chisels (above and beyond something like silver steel rod). A2 is not a great chisel steel, O1 is decent, but a silver steel rod in the 1.1% range is probably better (Slightly harder/stronger but tougher at the same time) than O1. The more plain the steel gets, the faster it will rust.
A2 doesn't move much when you heat treat it, which makes it better for makers (it's also not that tough), and when you get it from someone like LN, they drive the hardness up a fair amount to about the same sweet spot as O1, but the chromium does something for the maker and nothing for you other than make a chisel that lasts about as well as O1 slower to sharpen or grind chips out.
Drill rod and plain steels, on the other hand, require a lot more follow-up grinding. To the point that over here, LN's heat treater gave up. That's the world we live in now- the tools are made in CNC, the customers count a thousandth of an inch, check their chisels with a digital caliper and proclaim surface finish.
All that said, if you get the wood handled footprints and they're not defective in any way and sharpen them with oilstones, you'll never have trouble with rust and never really want for anything better unless you like to hold up the chisels by pinching the tips at the bevel (that's dippy, anyway).
