To your first point: I'm not sure this answers the poster's question, as the poster was asking why yeast have been shown to be much less viable when rehydrated in wort as opposed to water. I did not listen to the podcast you posted, but the guy Sean Terrill that it references is actually the guy who did the experiment that I linked in my original post, that experimentally showed viability was reduced. This result has been repeated in different lab environments, and is well known.
It seems that you are arguing the point that good beer *can* be made without rehydrating, as that's the thesis of the article you have referenced. I agree with your point, as fermentation quality is much more correlated with yeast pitch rate and fermentation temperature than whether or not one hydrates dry yeast in water or wort. As you said above, yes, if your yeast has 50% less viability when pitched into wort, you can just double up. True, but why be so inefficient? Why spend twice the amount of money on to hit an optimal pitch rate when you can spend 2 minutes re-hydrating a package of yeast while you're chilling your batch?
As to the article you referenced: while I appreciate the experiment, apparent degree of attenuation is only one piece of the story from a quantitative standpoint. I think for a quantitative analysis to be convincing here, you would need to measure the amount of a number of relevant flavor compounds in each beer (e.g. esters, diacetyl, etc.). Further, 12 "average" tasters trying the two beers side-by-side and indicating their "preference" is not very convincing as a final result. "Preference" doesn't matter here; the author himself said that his perception is that the non-water-rehydrated beers were fruitier. I think better tasters (e.g. BJCP certified/national/master level judges) would help the qualitative/perceptual part of the story, as they could specifically identify differences between the products. To me, what is more convincing is the academic literature I referenced.
As to your second point which was "why would an advanced brewer use dry yeast?", dry yeast offers a number of advantages over liquid yeast. First and foremost it has a much longer shelf life if stored properly, but I think you'll more commonly hear homebrewers talk about the cost effectiveness of dry yeast. For instance, a sachet of US-05 contains about twice as many cells as a vial of WLP001 at a little more than half the cost. Those, to me, are the primary reasons to use dry yeast. Liquid yeast is also great, and has its own advantages, so both are very reasonable to use at both the homebrew and professional levels.
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Oh, and don't put sugar in the water either. Just plain-jane tap water.
