I don't know about crazier.
Mkhitaryan's stats were 11 goals and 15 assists in 31 games as a 26/27 year old.
Sancho is on 17 goals and 16 assists
in 25 games at 20 years of age.
Sancho is at an age where he hasn't reached his peak and should continue to improve, whereas Mkhitaryan was the finished article and couldn't cope with the step up.
Think of it this way, Martial (24), Rashford (22), Greenwood (18), Sancho (20).
Players don't decline until they hit around 30-31 generally, with 28-29 the peak.
Martial can be released in 7 or so years, but until then the players will only grow together and become a force.
The front 3 will be lethal, AWB is 22, Maguire has 5-6 years in him, Bruno is 25, Pogba 27 (both as midfielders can go perhaps 6 years).
The team can be freshened up when needed but the team itself will only get better now.
Scary stuff how the team looked to have no plan and direction now its like the clouds have parted and you can slowly see how good the squad is.
In my eyes the team is nearly good for 7-8 years with fresh faces bringing in now again, what the team has is a very good spine.