I dont think rotors are cast iron - they seem to be a nice chrome alloy steel. Ive never seen my rotors surface rust like a car, if I dont ride the bike for a few months.
The brake pads wear down the rotors. I think ceramic pads wear the rotors the fastest. Normally you can get at least two sets of pads on a brake before you have to replace the rotors.
On cheap car rotors the bulk of the metal is cast iron, and they plate on a better grade of steel just where the rotors contact the pads. Once that layer wears off, your rotors look like nothing but crusty rust.
I measured the rotors and they are at 4.5-4.6mm with some tapper wear. The pads are 1-2mm. If I'm not mistaken discard thickness is 4.5mm. The bike is ridden hard. I ride it to work on a really busy freeway which has lots of stop and go. Otherwise I would've just thrown a set of pads at it.
Motorcycle brake question .... Using the front brake & under 5mph, it feels like the front is rocking like am I on a sea horse. Not horribly. Just enough. When I brake hard. It is fine. When I use the front and back together its fine.
Should i start with replacing ... All front pads > Front rotors > rebuild calipers > repair/replace front fork legs. (I have bled the from and rear lines.)