Claudius how many goals do you get from Havertz, how badly do you suffer with injuries, how much more strongly can you finish games, how much more flexible in a tight schedule, how many more systems can you play? It's not about 5 goals or 15, it's about having a better team that can compete across all competitions. I'm the last guy that'll kill a manager for spending money.
Also, criticizing retaining a player has nothing to do with their price. Should have sold Jesus, but I'd never say he shouldn't have bought him to begin with.