I’ve always thought that getting a mix of distance and sprints only helps athletes. While the distance running may not precisely help for pitching, it can be beneficial as part of a total conditioning regimen. I’ve found that distance running helps clear my head and puts me in a positive mindset. It may not add velocity to your fastball, but having a clear head, being positive, and focused has benefit for pitching.
It’s sort of like tee work for hitters. If there is nothing wrong with your swing, the tee work does nothing to make you a better hitter because the skills used in smacking a ball off a tee do not translate to hitting a pitched ball. Some people still hit from a tee as part of their routine for many of the same reasons–it won’t hurt you, and if you enjoy it, get some mental benefit from it, and can spare the time, go for it.