There is an alternative theory.
(1) Lift is generated by expenditure of money (otherwise termed reverse reaction to lightening of the wallet.)
(2) Lift required is not actually proportional to weight, it's proportional to beauty.
Hence a glider, tends to need very little money to generate lift - and the more beautiful it is the more lift it generates for less money.
Your average light aircraft needs a moderate amount of money to generate lift.
An airliner, which only it's mother could love, needs large amounts of money to make it fly.
And a helicopter, which is so ugly it's mother hasn't made her mind up yet, and probably never will, needs astounding amounts of money to make it generate lift.
Unfortunately like all other models it breaks down in places. Firstly it ignores microlights - which are ugly but generate lift very cheaply, and harriers which are very beautiful but need lots of money to fly. It also ignores purchase cost, which is almost completely unrelated to flying cost.
So why am I spouting this line of airbollox. My point is that virtually all scientific / engineering theories are just models. They are there to allow you to predict what happens under certain conditions - even the one I've just given. The really clever aerodynamicists actually probably don't understand lift better than a PPL who has passed his technical exams - what they do know is (a) a lot more different models, and (b) the limitations of each model far better than anybody else. That allows them to know which model or set of equations to use, to predict what they want under any given circumstance. The really clever ones can take a combination of models and generate their own to predict an aircraft's behaviour under particular circumstances.
G