Interesting.
I think it important to also remember that the average height of the Japanese has increased markedly over the past 100 years. Many swords just under 2 shaku were just as likely to be used by samurai who were smaller in stature as a practical matter. Even in WWII we see many gunto made right around 2 shaku.
I would think a good place to get some actual data on this would be to look into the records of sword production said to still survive. Perhaps in the records of the Tadayoshi/Hizen Daimyo or some shinshinto smiths there exists details about who the swords were ordered for, specifically.
We do know the economic fortunes of the ruling class deteriorated as the Edo era ran its course, with samurai became more and more indebted. As a result, we also know that swords were sold, pawned, etc. No doubt wakizashi formerly ordered by samurai ended up in merchant hands as time advanced.
We also know that Daimyo and the upper levels of the samurai class were indeed able to afford wakizashi and kodogu by the top artists of the Edo period.
Thus, it is quite uncertain when it comes to many wakizashi to determine exactly who owned and wore them through time. This is what the price differential addresses- the uncertainty. WIth daito, there isn't this uncertainty- daito were exclusive to the ruling class. There is no conjecture, no theory, no doubt.