Slim one of your comments sticks out to me here..

The one about Robinson and Moore etc with 100+ KO's on their record, flat strap from bell to bell and dynamite in their fists...

Tell THAT to Manny Pacquiao (regarding workrate)
Tell THAT to Gennady Golovkin (regarding dynamite)

And as for the 100 KO's, the reason is the same as for WHY they could perform as they did perform...

They fought opposition so abysmally poor, hardly any if any of them would ever step foot in a boxing ring with a top rated professional, let alone not get knocked out well within 12, let alone 15!

Obviously nobody could have so many fights against good opposition.