If two people of equal strength do the same exact workout, using the same exact poundages, for the same exact amount of reps,but it takes one guy two hours to complete,and the other guy only 45 minutes to complete,who trained harder?
More work done in less time = intensity of effort............. and using intensity techniques such as pre-exhaust,drop-sets,super-sets,tri-sets,etc.etc.,and a good mind muscle connection =a far better way to train than to just simply slap more plates on the bar.
No one can increase their strength forever without hitting a ceiling.