Leg strength is extremely important. I have not seen pitching gurus like Driveline or the TX/FL Ranches talking about doing any exercise bike workouts, however rigorous, to achieve that leg strength. But I would definitely defer to them and research, what, if any, bike workouts they'd recommend.
I've seen them discuss explosive running (sprints) but not long distance running. Again, I'd ask the pitching gurus!
A large middle aged man like myself though...I need a Peloton workout now!! Perhaps a 45 minute 80's classic rock ride this afternoon.