Scenario A: The pitcher goes six innings (commonly considered a quality start, but already becoming more rare as pitch counts are reduced and most starts only last five and change). The DH is removed, resulting in the need for a pinch hitter - or the pitcher bats - at least one, often twice. If the team gets lucky, the DH made the last out and they’re leading after 8 1/2 innings at home, but even then there’s a decent chance of at least one AB for the “pitcher’s spot”.
This is more or less the ideal, and is reasonable.
Scenario B: The pitcher goes five innings, which is pretty typical today. The “pitcher’s spot” likely comes up two or three more times. That means two or three pinch hitters.
This is starting to get questionable under today’s roster restrictions which only have 13 position players, including the DH.
Scenario C: A bullpen game that runs through six, perhaps even eight or nine pitchers. Your DH probably starts as a bench player so your best DH can be brought in to hit in a big situation. With five position players in addition to the eight regular starters, you’re almost certain to have to use all five to hit through the course of a game. That includes your backup catcher, so you better not have anyone get hurt during the game. And that it’s over after nine innings.
Unless the roster rules are changed, this scenario just doesn’t work.
Outlook: You might as well go back to having the pitcher hit, and that is a complete non-starter for the players.