Warren in Lancaster, PA
I think it is wrong to assume that older tools were more highly tempered because of less skill or less sophistication. It is very easy to get a harder tool: just temper at a lower temperature. Yet the historic makers who made tools for professional woodworkers probably tempered to a hardness closer to old Stanley than to Hock. Moxon (1677) notes that a "dark goldish Colour" is used for tempering edge tools and similar temper was used into the 19th century or more.

Today people read on some blog that a plane iron should be thick and hard, and so they make that kind and brag about. It is not like they know what they are doing.