You could build a functional team out of R team if you so wish to. The key is going to be your selection of EX skills and souls.

While I have yet to clear a rag content with my fire R team (or any R team for that matter...), I believe with better weapon grid (currently fire is at 75% assault) I should be able to do so, and besides with tower coming sometime inn the future, you'll get the opportunity to use a majority of your himes anyway...