I don't understand the obsession people have of building the team around a single player. That makes sense if you have Messi, Neymar, Suarez, Ronaldo, Bale, etc, in your squad, but very few players in world football deserve to have the team built around them at the highest level.
All we have to do is have a strong spine, and we're not far off with the likes of De Gea, Bailly, Lindelof (hopefully), Valencia, Pogba, Herrera, CM?, Rashford, Martial, Mkhitaryan/Mata, FW?, Lukaku.
We also probably need a left back, unless we're going to persevere with Shaw (I feel like I've typed that sentence word for word a hundred times in the last few months), a forward of some description who can guarantee goals/assists, and probably a midfielder for depth, though a Fabinho type who'd challenge as a starter would be better for obvious reasons. I wouldn't say no to Matic though.
Anyway, back on topic, Martial is young and inconsistent. There's no telling what kind of season he's going to have. It could be 15/16, or 16/17, or better/worse than either. His mentality could be an issue (as an outsider looking in, I would guess that last season it was an issue), but the kid is clearly incredibly talented. If he can translate that into work-rate and a better mentality (by which I mean, a Mourinho type mentality), then he could be phenomenal.
People want us to sign teenagers and players just reaching their early twenties. Well, this is what you get when you sign those players. Inconsistency. That's the joy of watching a player develop at your club. He might make it, he might not, but you don't write him off until he's out the door.