I have a different view. I think he is going through what I call "the Martial phase". When we first bought Martial, he was very good. Then he tapered off for at least 18 months, maybe more. The odd good performances here and there but nothing consistently special. Then all of a sudden he is now unplayable.
De Gea is the same. When we bought him he was not very confident and then had a few seasons where he basically saved our skins - week in week out, despite having Smalling and Jones in front of him - we were singing his praises every single week, just search for those threads I am sure you will find them. He is now back to having a bit of a less than excellent time, I do not think he is shite, far from it. But he has made some errors. I think people who think he is shite need to have better memories of his good moments too in order to make a fair assessment. He needs a bit of an arm around the shoulder and support from Ole and all of us and I am sure he will be back better. Do I think he is a shoo in every week now? No. But do I think he is "shite, we need to sell him now" ? No. Goalies are scrutinised more than forwards i.e. if Martial had as bad a run as De Gea, it would not be noticed as much.
I would tread the Henderson topic with caution - he is unproven at a big club, and although he has played well at Sheffield United, the pressure is nowhere near the same. He might still be good for us, but to think it is a given that he will succeed here is probably unwise. Remember, the goals that he ships at Sheffield United (and when they lose the game) will not be scrutinised as much as De Gea making an error here and there at United and us still winning the game. That's the difference in benchmarking.
Romero probably should be given more starts - I think he is a safe choice for the interim to let De Gea know that he is no longer a shoo in, although we do not think he needs to be sold yet.