These new actions are machined from chrome molly steel instead of stainless. Is it that big of a deal that it isn't stainless? Aside from the corrosion resistance if left uncoated, does stainless have other properties that make it better than chrome molly i.e. stiffer, stronger etc. ?
There are a ton of different types of steels. Even a ton of different types of stainless steels, and there are a ton of overlapping properties of them all. That said, I think the biggest influence is how the particular steel is heat treated. That's what makes the difference between 50ksi yield strength, and 200+ksi yield strength with the exact same blend of steel.
On the whole, stainless steels are not as strong because the chromium content is pushed up to form protective chromium oxides on the surface. The chromium isn't as strong as iron. That said you can certainly have martensitic or precipitate hardening stainless steels that are much stronger than certain non-stainless steels. Again, this is very dependent on heat treat, geometry etc. Without writing a book, material variability is a real thing, Carbon content is the main driver of strength, and proper heat treat typically influences properties more than the type of alloy. (ETA: Strength isn't the ONLY thing to look at. Toughness, wear resistance, etc.. can also be extremely important).
Corrosion resistance is the primary reason you see stainless steel actions. I think with Cerakote, Nitride, proper maintenance, it's mostly a non-issue. I prefer chrome-moly or alloy steels to stainless for the most part because stainless in most cases has a higher susceptibility to galling/wear which I find more worrisome than whatever minor surface oxidization might happen between maintenance cycles.
For barrels, stainless is really nice. Not having to worry about bore condition/pitting etc. is worth it to me. Actions/bolts/etc., ehh not so much an issue.