OK.
My provided song, "Lost without you" has a clearly defined, clearly pronounced tonal chord progression.
It is a simple and clear example of a FUNCTIONAL HARMONY:
ii(7) - V(7) - I(maj7) - IV(maj7)
The chords from that song have functions.
In my provided example, the tone center is imposed by the chords and their progressions.
"If the song is in C major, the fact that you start the C major scale on a D does not mean the song now all of a sudden becomes D Dorian," but...
For a guitar player who is trying to solo over that chord progression, the fingering pattern of this/that MODE is a big help; therefore, our guitar player would decide to use the following modes with those simple function chords.
(Dear guitar player, have you googled the term, "diatonic?")
With the Dmin7 chord, the guitar player would use the Dorian (memorized) fingering pattern, with G7, the (memorized) Mixolydian fingering pattern, etc...