This myth that guys can no longer be athletic with added muscle really needs to end lol. If you’re putting on the muscle correctly it wouldn’t have any negative impact on your coordination.
Nobody is putting on 10-15 pounds of lean muscle naturally in less than 6 months anyway. Its why I always scoff at reports of players adding 15-20 pounds of muscle. They may have put on 15-20 pounds and some of that is muscle but its not all. Not even close.