Manufacturing quality matters, too. Cheap stainless steel (e.g. basically anything from a Lowes or Home Depot, or elsewhere standards aren't rigorously enforced, like so much exterior cladding, trim, and fasteners on modern construction) will often rust almost immediately in spots as the alloying isn't sufficiently homogenous or pure. See https://en.wikipedia.org/wiki/Nickel_pig_iron

What do the numbers mean?(slightly confused because your description of 316 makes it sound generally more badass than 304, but I can’t fit that in sequence with 430 being the worst).

soooo only the first digit in number matters ? rest look pretty randomly assigned

The first is the category / blend of metals, the latter represent the amount of alloy metals.

And more “badass” to machine than 304, too. Not for amateurs or flimsy machines.