Lots of ways to get a stable bench top.
Hm's bench is typical of long lasting bench's that will last 200 years.
I really like heavy frames, 1.5" of plywood, glued and screwed together. Recently found just how good the Commercial doors are for heavy shooting bench tops. Habitat for humanity is a good place to start for these used commercial solid core doors, they are very, very heavy.
Old counter tops are a big plus, but they don't take the hard abuse that a 1.5" plywood top would take out in the garage.
I am still using my first reloading bench/cabinet built in 1979, 4x6 frame, 1.5" plywood top with some overhang, drawers below, and shelves above. The unit has been moved 6 times, still as solid as the day it was built...glue, screws, lag bolts.