Great topic for discussion. As much as I support the mask issue, I doubt that is having much effect on the number or quality of pitchers.
Let me throw out a theory. This game used to be dominated by pitching. Pitchers were the players most willing to work the hardest and were rewarded for their work by being the "stars" of the game. With 40' pitching distances, they could blow batters away. But then hitters started working harder on their game ... lots of hitting coaches surfaced to meet that demand. The mound moved to 43' and the bats got hotter. The scoring of the game increased, and hitting the ball hard is more fun to most players and their parents than learning to throw balls that move to spots, and sometimes getting them pounded on by good hitters. Meanwhile, a lot of college pitchers don't get to hit much, if at all. And if you're not one of the top 2 pitchers on a team ... travel, high school or college ... you seldom get to pitch either.
Some of those top athletes who pitched in the past have decided to be hitters instead, and those who are still pitching are now facing those good top athletes. The pitching may not be any worse than it was, but it certainly looks worse.
Just a theory ...