RE progressive overload, anyone that says it doesnt matter doesnt even understand the basics when it comes to muscle growth.
Yes and no one even really believes it doesn't matter, no matter what they say. Almot every single bodybuilder trains so heavy they can't even perform proper reps. If load didn't matter, if we really believed it, we would all stay home and curl a broomstick. On a few grams of anabolics even a broomstick would be enough for a pump.
As far as making gains, the fact of the matter is that we all stay the same or regress most of the time. Me, you, the pros... we spend most of our time in the same fucking place. Take a look at the top pros, most have been sitting at the same muscular size for years and years. Gaining new muscle after those initial gains from a new training stimulus or drug stimulus is HARD.
It's hilarious to hear some pro say "all that matters is stimulating the muscle, the weight doesn't matter at all". Meanwhile the guy hasn't gained a single pound of muscle in a decade. "But, but, what about Serge Nubret (insert any pro known for training 'light')?" Well, how much muscle did these guys gain in the last 10 years of their careers when they continued to train using the same load and volume (assuming they didn't start a new drug such as GH or insulin)? Jack shit is usually the answer.
Like anabolic says, you can clean up your style of execution, increase volume etc and make some gains but the main stimulus for growth is still the load (within a certain rep range, everything else being equal).