Dempsey Roll is the best technique suited for a boxer like Ippo. Coach canβt just train Ippo to be a counter puncher or something. So he was delaying the fight until Ippo gets all his βstatsβ (attack, defence etc) higher. Imagine seeing Mike Tyson trying to jab and counter, just wouldnβt be effective. Same applies to Ippo.
Coach is harsh because heβs worried if Ippo fails then he might just give up or be so mentally destroyed if he loses that he wonβt be able to recover.