In my youth, standing and 'dancing' on the pedals was as natural as breathing. I could also pull up so hard on them that when I read somebody recently who said that analysis of racers show they don't really do that (pull up) I was (and am) simply incredulous. Back then the consensus was that standing was not necessarily less efficient, but that it did use more energy. Standing was a standard technique for jamming up short hills without shifting down, usually done gripping the brake hoods and applying opposing forces to them, pushing down on one while pulling up on the other, to move the bike side-to-side underneath - the 'dancing' part that reduces wasted energy spent holding things rigid.

Back then, frames or parts that broke were either defective, or cheap pieces of crap no matter how much they cost. The term 'weight weenies' didn't exist, perhaps because putting people down during ordinary discourse was not quite as in fashion then, but such people typically paid a price in dinged rims and broken spokes. Jagged daggers formed by broken parts would have been regarded with horror.

Now, back into cycling at 63, but with hip replacements and greatly diminished flexibility, I don't have the confidence to pedal standing - yet. Part of that may be not trusting clipless pedals yet, either.