I can dig it, as I had several 70's dirtbikes and street bikes- but in both areas there really were significant improvements right around 1980 +/-. On street bikes engine/braking was important- on dirtbikes I think suspension changes made the biggest difference.
One of my favorite dirtbikes I owned was a 1983 Yamaha IT250
Here are 2 pictures- the top is earlier, the bottom is later.
Like everything I own, I heavily modified it. Suspension, clutch, gearing, ported, bored, pipe & silencer, carb was bored tall oval (more flow WOT but no loss of tq), crank had slots cut in it (back then they claimed this helped the gases in the crankcase..who knows if it was true)...etc etc.
It is one of the only things I kept when I went into the Army in the '90s but shortly after I returned home after my service someone stole it out of my apartment yard.

Loved that bike.