To be honest, OOP never really seemed like a good fit for R. Functional programming is a much more natural fit, given that both it and R come from a mathematical point of view. R is a great language for the mathematical/statistical stuff it was invented to do, but I don't think it will ever be a general-purpose language, and it probably would become worse at its core purpose if it tried to. More work on being easily…
Functional programming is not orthogonal to object oriented programming, they are paradigms that can be used together and the popular object system developed in Java is not close to the only way to do OOP. R, like Common Lisp, uses an OOP system based on generic functions (well, one of many OOP systems in R, but that's a different topic), where the function handles dispatching to match the object. Effectively instead…
This reflects a very deep misunderstanding of the distinctive characteristics of each paradigm. It's so far off that it's "not even wrong".
Functional programming is much more about things like purity and referential transparency, about composing functions and/or combinators, about a particular way of managing or modelling effects, about a way of thinking, about using certain kinds of data structures and algorithms.
It's not a syntactical difference.