Learning Japanese fast - Why not use frequency lists for 80% coverage?

Most people here seem to attempt to do most of RTK first before studying the readings, compounds, and words. I personally suspect it is faster to learn a fundamental set of things before building on that, such as learning compounds and readings. I think learning multiple things at the same time slows things down.

Also, I realize that for an 80% or 90% kanji list, it would still need to be cross-checked against an 80% or 90% word list to find out if there are some kanjis that need to be included before being ready to study the relevant word list.

EDIT: Or what the administrator said