I disagree, lots of steels I work with are over 1% and not just the new high alloy steels; old black diamond files were 1.2%. They work like steel.
I will agree that some of the high alloy steels will cottage cheese on you like trying to forge cast iron (H13, D2, etc) but they are not a cast iron as they don't have carbon in them as graphite but rather as complex carbides. (May we leave white cast iron out of the discussion?) It's the graphite that makes a "cast iron" in my opinion!
Semi steels, nodular cast irons, etc still have graphite it is just in roundish forms rather than lenticular ones.
Puddled steel is a method of going from cast iron to wrought iron only stopping somewhere in the middle and items made by that methodology will be forged to shape and so should show forging rather than casting tattletales.
Cast iron has a lower melting temp so if your foundry is not controlling the carbon content it's wasting fuel and putting a greater strain on the refractories as well.
The line is a bit murky these days with some high alloy steels up there at the 2% C line; but as I previously mentioned no graphite!