Putting together a 'new' Best Of The Doobies quad if one never existed before would seem an odd choice to make unless it was just done as a cheap way to charge more for the set.
At least with Chicago IX, the title already existed in quad and there are some different edits on a couple of tracks. Then again...there is a shorter version of "Listen To The Music" on "Best Of"......
I completely understand your point of view, which is basically a purist's argument, but I would only be in favor of doing such a thing if a "Takin It To The Streets" Quad mix does indeed exist because then the original 'best of' track list and artwork could be used for this new Quadraphonic edition (while also including the stereo GH in high-res too.)
And even though this would be an unprecedented move where Quad was concerned, Audio Fidelity did have to do the inverse of this for the 'Best of the Doors' SACD by creating a stereo master for a compilation that was never released in stereo.
But hey, if such a set comes to pass that has just the 4 released Quad mixes, that is completely fine with me.
Anything else is lagniappe.