The comparison I was making between classic rock and walking bass lines in big band music as follows: think of Smoke in the Water, with the bass playing in octave/unison with the guitars. Also, think of those block chords in Pinball Wizard, etc. Generally speaking (yes, always exceptions) in this type of rock, phrases are usually neatly grouped (2 or 4) & downbeats are almost invariably hard & completely unsuppressed. With the bass supporting the chords in such a matter, he can still fill in, or "roll" from one chord to another, but structurally & texturally there's a certain level of homogeneity involved. The point is that a strong punchy sound in the bass helps drive things & provide a solid foundation.
Now, think of Four Brothers by Woody Herman. The walking bass lines are a little more separate from the highly rapid unfolding melody played in block harmonies by the sax section, with syncopations strongly accented by the brass & drums. It's more fluid & stratified. I referred to this earlier as "almost contrapuntal". Think of the High Baroque! Think of all those movements from cantatas, suites (orchestral or keyboard) by Bach that have lilting or bright walking bass lines. Think of arias or movements from Handel's operas, oratorios or concerti that are supported by walking bass. (Arias technically fit a definition of homophony--melody over chordal accompaniment--but the presence of a walking bass certainly puts it a step closer to polyphony.)
When a musicologist refers to Mahler's Eighth Symphony as "polyphonic" again, he is making a comparison to other works, say, Brahms' Tragic Overture, or Mahler's earlier Symphonies 1-4, which do have counterpoint and are texturally stratified, but far less so.
My undergraduate studies were largely in musicology, but my degrees were in orchestral conducting.