1. Having the runner leave when the pitcher is standing on the pitching plate is noticeably designed.
2. Switching pitchers isn't noticeably designed. We know why it is happening, but it isn't designed to stall/hasten the game like leaving early is designed to do.
3. Switching pitchers EVERY PITCH is designed to delay the game.
4. Having batters swing at every pitch (including the ones that roll across the plate and pitch outs) is intended to speed up the game.
SIDE NOTE: Umpired the games last night, and with a 1-0 lead, home team gives up 3 in top of inning. After 1/2 inning his team hustled, other team hustled and he had his girls swinging at everything close to the strike-zone (most were). Girls ended up scoring 3 runs and winning 4-3 in bottom of inning when time expired.
After game, coach asked me if he could have stalled out the inning and still won the game. I told him no, but he could have patiently batted and called his offensive conference, put in pinch runners, etc., ALL LEGAL PARTS OF THE GAME, in order to "make his situation better." He liked that.