Stainless generally is tough but not rigid or hard. Good alloy steel might have a tensile of 200000 PSI and a hardness of RC55 to 60. Good stainless might be 100000 PSI and a hardness of RC35 to 40.

It's hard to drill and cut. Welding can cause cracks.

Bottom line, what makes stainless hard is chrome. Most ss alloys are about 18% chrome. But this is mixed with about 8% nickel which makes it tough but also soft.

Chrome Molly tubing will have no nickel in it; it's replaced with Molybdenum. It has all the hardness from chrome and the moly keeps it from being brittle and improves stability after welding.