Imperatives mean imperative. They are not named: esstential, reccomended, optional, etc.
They are something every good golfer does and that is why they are imperative. Could you play golf without them? Yup, but you may not reach your potential.
Sure, you could eventually become scratch...however the 3 imperatives make a golfer consistent. You could play with a flip and a bent left wrist if you do it all the time constantly. It's just going to be difficult.