Well, fair enough I guess you could argue that waiting with even basic grammar until after RTK doesn't have any huge merits. But to turn it around, doing them in parallel doesn't seem to have any merit at all in my opinion. Also, sure you don't need 2k kanji for JLPT4-5 or to do grammar, but since the order of the kanji in RTK is not most used to least used, but completely centered around the primitives, you basically have to do the whole book to run into all the really useful ones.
The only grammar I ever studied was Tae Kim's guide, and at least for that I think that it is not only super easy words and kanji that appears and that having done RTK before will certainly be very helpful.
The only grammar I ever studied was Tae Kim's guide, and at least for that I think that it is not only super easy words and kanji that appears and that having done RTK before will certainly be very helpful.