The musical reason for the "4" accent is.. its the signature note emphasised by the tumbao and base, which is dominant in Son rhythms , and Son is the foundation of todays latin dances . Even a "slap" by the conga on 4and1, may often be heard,and if not heard, is always implied .
The " clave "which is incorporated into the phrase , is often debated whether or no, it occupies 2 bars .Sometimes yes, and sometimes no .
The 2 major forms of Clave are " Rumba and Guaracha " both in 3/2.. also.. " Son and Guaguanco " , which are in 2/3 .There are also other clave signatures, as in Guajira and Montunos
NB.. The Rumba I quoted is NOT the formalised one that is dance in partnership, but, the indigenous style which is danced solo.
Clave rhythms, are the " Alma Y corazon "( heart and soul) of latin music.
Bottom line.. the many layers of latin music, gives us the opportunity to express the music ,as our ears perceive it .