I can see that we just really disagree about this, and I can respect that. I think that you're wrong, and that you're unfairly criticising one of of our better players to an extent that you'd be happy to see our team weakened as long as we sold him, but hey, you gotta have confidence in your opinions!
Honestly, one reason why I think it's essential we keep Martial is that, with the exception of Cavani, he's the oldest forward we have and the only one over 24. Him, Cavani and Rashford are the only ones who have overcome adversity. I have faith that Martial will come back stronger after last year's disappointment because I've seen him do it before. He is used to receiving heavy criticism from Manchester United fans, and the national media, and coming back stronger. If you sell him then you're putting that same pressure that's normally on him on Greenwood and Elanga. United fans and pundits started criticising Martial after he didn't score for 2 games last season. I don't want us to feck with the development of our youth by putting that pressure on them this season.
Greenwood has played a few games at 9, but has never looked particularly comfortable or effective there. His best performances have come off the right, while Cavani or Martial have played at 9 and held the team's shape. To ask him to be our main goalscorer from 9 while also holding the shape of the team, in the way Martial and Cavani have done, is a lot. We don't know how he'll deal with that pressure when he hasn't scored for 3 or 4 games in a row but he keeps getting played at 9 because we don't have another option. We know how Martial will do though.
Elanga will not play at 9 this year unless we are desperate. And that's right. Greenwood is a natural 9, and he spent his first year learning the game from the right, where there's less pressure and less heavy challenges. I really think it's crucial to protect our young players if we want them to be successful, and that means not putting loads of pressure on them by asking them to be out main goalscorer/focal point in a campaign where we're expected to challenge.
No point in reading too much into pre-season form, otherwise we'll be starting Pereira, the pre-season Pirlo. I think you're reading far too much into pre-season form here. From my eye test, Greenwood has been sort of lethargic and hesitant for much of pre-season and Elanga/Lingard/James/Pereira have all looked sharper. None of that changes the fact I'd start Greenwood over all of them. And I thought Martial looked up for it on Saturday, especially considering he's just back from injury. I saw him putting in energy and aggression to win the ball back high up, as if he had a point to prove. That bodes really well for his attitude for the new season.
Again, I disagree with your review of Martial. It's more like he's on form for a year, during which time he's about 50/50 to score in any game. That was his form for 2019/2020. Or he's off. When he's been on in his career for us, he's more or less on a par with any striker in the league who's not called Harry Kane. And I mean that over the course of a season. And he's better at scoring important goals than Kane.