Everything I've researched over the years (plus the reports & recommendations of healers I've studied using tinctures) indicates glycerin is a much weaker solvent than alcohol...which would create a much weaker tincture.
But I'm always willing to learn & UNlearn. So please post/share the source/s you've got that indicate glycerin is a superior solvent to alcohol (which would create a stronger tincture)...along with any testimnoies from healers using tinctures in their clinical experience that opted for glycerin over alcohol.
Also noting - the shelf life of glycerin is less than 5 years (in many cases, the shelf life is reported to be less than 2 years).