There’s an issue of actual principles at play. Remember, Zcash was created because Bitcoin was public. In a very real way, the entire point of Zcash is to drastically reduce the number of transparent cryptocurrency transactions in the world. It’s incorrect to reduce Zcash’s principles to number go up for shielded.
Although utilitarianism is useful for meeting principles sometimes, it’s dangerous for setting them. And you just showed why: What would we do if increasing shielded transactions in zcash by 2x increased Bitcoin transparent transactions by 100x?
Given that we seem to have totally lost track of Zcash’s principles as a pointed out in the thread on resetting zcash, yes we need this principle. We need to reaffirm our beliefs.
As to the question of evidence, I thank you for proving why we need principles.
Of course there is no evidence, because no one has tried. Instead they’ve grand standed on the kind of technicalities you made above and a mistaken belief in “the best of both worlds.” And they have removed warnings from the wallet SDK about transparent transactions exposing your data. This is the logical conclusion from acting without this principle.
There’s reason to believe a principle of depricating t2t transaction may work as I described in the original post up top. It might not work. Principles don’t exist in a vacuum and we have multiple. We should not follow this one when it conflicts with the principle of increasing shielded usage. So if it does cause the harm you imply, then we stop and re-evaluate. We aren’t robots.