Given how the Atlanta Braves started off with their relievers in 2019, I'd shudder to think how such a rule would have impacted the season. At times, it wasn't good regardless as many batters were added up thanks to excessive walks.
The relief pitching role has morphed over the years with some pitching developing more of a specialization role that has limited their use to 1 or 2 hitters at a time... hence the impetus that has brought us to this point.
Adam Kolarek of the Rays and Dodgers, for example, led the majors in 2019 with 42 game appearances in which he faced 2 batters or less (out of 80 total games).