So... while in-person at the Esri UC a few weeks ago I took the opportunity to "gripe" about this issue at the Pro product island. I had nothing but great interaction and engagement with Alycia regarding three topics we discussed, of which this was one. She briefly left and came back with another employee who could shed some insight on this particular issue.
It turns out that this other employee (I won't name but he was great as well, seriously!) was the person that argued for changing it to one decimal place (who could have predicted that?). His reasons were sound, though shortsighted (my opinion).
I requested a reversal to 6 decimal places (quick, easy, not much testing) or, better, an option for us to specify the number of decimals shown (obviously more development and testing).
While he made no absolute promises, he sounded positive that they could just revert back to 6 decimals. I think they just didn't realize how people are using that information. It will be discussed by the Charts team. If it happens, we likely won't see it until Pro 3.1.
I'm keeping my fingers crossed, but I'll believe it when I see it!