Fortunately, there are a few top-down views of the at bat. Here is one that is rather telling:
Pinto was a good distance behind the back line of the batter's box. I thought, at first, Pinto had come forward to block the ball. Based on the position of the umpire, he simply dropped and tried to block the ball (poorly I might add).
The issue is that Bauers' follow through is well outside the batter's box. Unfortunately, this is the only picture I could find of the infraction:
Pinto's head went down which is proper, but probably wouldn't have affected the outcome anyway. I know there are a lot of hitters that use the top-hand release method. Remember this guy?
As mentioned, catchers didn't necessarily try to steal strikes back in McGwire's day. However, there is a risk / reward. There is a risk to the catcher that he might get hit by a bat. If you don't want to get hit, sit back six inches or don't meet the ball to frame it. Not sure legislating it would be the way to go.
From the batter's standpoint -- if Walt Hriniak is your inspiration, then you might hit somebody on the backswing. Should you be able to have your bat go back 34" behind the batter's box? You don't see that with hitters who don't release the top hand.
Did it suck the Brewers got the short end of the stick? Yes. Was it the right call based on the rule? Yes. Would it seem to make sense to have the catcher's feet stay behind the back line approximately 18"? That seems to be good, but I think Pinto was at least 18" behind.
Here is another picture that shows where the 18" line might go (from https://www.valleyafs.com/resources/baseball-softball/baseball-field-information/diagrams/batterscatchers-box-layout/):
Bottom line -- hit the ball, Brewers, and this isn't an issue.