Las,
You are confusing the two types of reshus harabim, פלטיא. Vs מבואות/סרטיא . They are treated differently regarding on how to define their reshus harabim, according to many.
In any case, rav moshe holds that 600k is defined by the habitants of the city, and that is how you have a platye.
Also, there are some that hold that there is really no such status of platye nowadays.
The orginal platye was an open market place type that was hefeker and was on the street open to all..
Regarding Ocean pkwy, I don’t think it has 600k passerby in a single day, as per the census.
Also, correct there are shitos that the 600k need to be עוברי רגל and thus cars are not applicable. This is the psak of the Bes Efraim (1:26 at the end, Yeshuos Malko of Kutno and the Marhasham