Nah! He remains a good manager he's just being unlucky with Injuries and some of the players available cannot help project his tactics.
What he achieved for the club last season is evident enough, you can't just right him off. I can recall the game against Barcelona very well, he read game very well and made good substitution ( bringing Fred in the guide the midfied ) Anthony was able to give Manchester United the winner. He got this issues when Lisandro Martinez got Injured against Sevilla. Building from back has worked for him in a way. Having no Lisandro Martinez behind makes that difficult for him.
Rasmus Hojlund ain't no bad player, have you asked yourself how many chances they've created for him? Just same way City does for Erling Haaland. I hate comparisons but Manchester United should do better with creating chances for the striker. ( I have personal issues with Rashford for not always passing the ball for Rasmus )
Now your idea of Wout Weghorst is wrong, he didn't score so much goals for United agreed, but he had a very high rating when it comes to work rate. They say he's lazy, but he's not too lazy to track down balls for Manchester United just like Rashford did against Newcastle.
I am pretty surprised that you still think he is a good coach and he's just being unlucky. He is just bad. And he will not be able to make Manchester United improve. In my opinion, he never was able to improve Manchester United. And now it is just evident. That's why people are actually losing their minds. In my opinion, he was never a good coach. He had no clear plan of what to do. He just tried a bunch of things and previously that seemed to work out for some reason. But now it is not working anymore.