Well that's not how you build players, unless you trust them and play them you cant take out their best and make them a world beater. They have those qualities specially martial. Also we have to think about the european competition. A better build up is more important than a goal tally's. Surely we cant get all of morata lukaku and griezmann next summer in one team.
A proper attacking build up and better penetration will make martial Mkh mata score more goals along with morata's numbers. A Creative attacking player llike griezmann improves the quality of the build up play which is more important than scoring number of goals against lower teams.
I don't like these ideas of building up youth and wait for all their mistakes till they develop to become a main starters. If we're willing to go this way we shouldn't be asking for any big trophies for some years coming. It may have been able to be done in the past but currently there are other 5 teams with a ready squad to challenge directly you can't be the only one who is waiting for some youth to develop you will be left behind by a far way from them. I don't care about Martial and Rashford playing or not, my only care is the team winning the league and that's the most important thing. The youth will get chances from the bench till the develop but we can't stop buying players because they might take their places ? It's not like we're getting an agins strikers, we are also buying 2 young strikers but more in their prime.
Finally, I agree with the importance of build up and that's why I prefer Morata over Lukaku but without good finishing up front you can build as many attacks as you want and miss all of them. We need both build up and finishing if we want to win anything significant.