Whether to use "whole" chords or "sevenths" is a style marker, to me, and can be individual style OR genre -- 7ths and 9ths are more "jazzy" to me, and ditto the minor-substitution-for-major (Dm for F, etc.). I quite often use non-7ths for the V chord, especially when accompanying fiddle tunes, flat-picking.
I am not fond of the "relative-minorization" of songs, though. That was the mark of a lot of songs in the Folk Boom, as I recall (it seemed that every song had at least six chords, major and minor, even if the original version had only two), and I grew to hate those. In fact, that's one of the things that led me to avoid "covers" of popular folk-songs, and to do my own accompaniments. I once opined that I didn't have a "style," because I did that "straight-ahead" accompaniment style, instead of the "arrangement" style some people use, and thought that the result was that I didn't have a "style." I was put right by Rita Ferrara, who pointed out that what I do with songs is indeed a "style."
So choice of chords, which ones to add, which ones to leave out, are a big part of "style," and can be a highly individual choice.