The Q was " WHY " the 4 was dominant..
and, I was probably dancing and teaching indigenous ( and BR )latin rhythms, before you were born ( IN the States with latinos )also trained with Laird in the 40s, and, DO you know Intern. Rumbas origins, and its antecedent ? and its NOT danzon.
ALL indigenous latin, in the Rumba genre ( an umbrella term ) is Son and Clave driven.
If you have a dis agreement with this, then may I suggest you take your posit to Salsa Forums, where there has just been a discussion on this very topic,( Son ) by NY latin musicians.