I believe he is a baritone. Bass singers in pop are almost unheard of now. For example the range he sings in for All of Me puts his break from head voice to falsetto somewhere near E above middle C which is pretty typical for a melodic baritone. read more
John Legend is a baritone. For starters, bass singers in pop culture isn’t a thing, especially nowadays. In terms of musicality, his lower register is not one that is of a bass singer. read more
The male voices are separated into, from highest to lowest, tenor, baritone, and bass. The highest a tenor sings is around a G above a middle C, and the lowest around a C an octave below a middle C. Tenor voices are used for solos in pieces such as Rachmaninovs "Vocalise" and Mendelssohns "Elijah". read more
Next the thing is that lableling a singer Bass alto barritone tennor is a very old way of classification and they dont really hold very true to this day with so many advanced techniques. No matter what the note is a singer can hit it so the classification started off so that people could sing in choirs and now most people sing solo or with a band so i guess you should just move past that idea. read more