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It hard to find fault or argue with a PhD Microbiologist!Just going by the "Yeast" book by Chris White and others' experiences.
The goal is to have sufficient glycerin to prevent bursting of yeast cells during the freeze/thaw process. Both sterile water and the liquid in wort dilute the glycerin to a concentration optimal to give this protection: 15% for sterile water, 25% for wort, though the other components in wort would lower the exact composition to something closer to 15%. Fifteen percent concentration of glycerin appears to give better cell protection than higher (or lower) concentrations.
In the final analysis it would seem that both processes give similar levels of protection. One difference I can see that favors using a sterile glycerin/water media verses wort is the
sterility. Wort by its very nature is a growth media for not only yeast but other spoilage colonies as well that would compete with thawing yeast cells. Infection risks would be less likely in a (mostly) sterile environment when attempting to propagate a starter from a thawed sample, even though the risk is probably quite low for either process.