Yup! The numbers don't lie -- 2/3 have at least one gap year, and around 5% of matriculants come from BS/MD programs, so that leaves around 1 in 4 matriculants being traditional. So, there's that.
Adcoms have been pretty careful not to discourage excellent traditional candidates from applying, since it is far from impossible to succeed. What they do go on the record saying is that they like the added maturity and experience that can only be obtained through gap years. Preferable is a loaded term, since some people are mature enough and experienced enough without it, but they are clearly in the minority. it also appears that, while all reviews are "holistic," high stats still count for a lot, so, at least at some schools, the higher your stats the less you might need the benefits provided by gap years.
Of course, YMMV! My only point in my response to your OP was that there was no advantage to staying in school if you are ready to graduate, in terms of the activities you mentioned, not so much that gap years were essential, or even preferable, for everyone.