I'd really like a citation for serifs being easier to engrave in stone. That really doesn't make sense to me. I'd expect things like runes -- entirely straight lines, minimal decoration -- to be easier to carve.

when you're using a chisel on stone. you need to hit it straight down, creating a divet (the serif) to get the cut started.

If you put the chisel diagonal and hit it with a hammer right off the bat, it just slides across the stone, and you usually hurt your thumb ;)

That doesn't seem all that implausible, but I'd expect the divot wouldn't need to be any wider than rest of the line.