What's more worrying is none "newbies" thinking that he is good enough. He isn't.
I have nothing against the lad, but to suggest that having better players around him will transform him into a #9 seems delusional.
That's the thing, he still looks at least potentially good enough, and plenty of games already you could take the "potentially" out of that sentence. Add to that this being his first season at a disfunctional club in a disfunctional team where no one was good enough, and it would be rather odd to single his underperforming out. Even Hojlund looked much better just the season before.
But it is delusional to think he would transform into a #9 by simply adding better players. Because the odds wouldn't be great to see him transform his whole approach. But that isn't the suggestion at all (outside of the few claiming it's all due to the lack of delivery by the rest of the team).
The idea is rather simple, he showed enough to suggest it's worth it to at least try to see how he matches up with two different partners up front. And since those look to be Cunha and Mbeumo (at least one of them is confirmed), the idea for many people is that the more direct/offensive players in the 10 positions change the responsibilities of the 9 position. They don't change their skillset, but they offer (or even request/require) a different match than i.e. Mainoo and Mount ask from you if they are the 10s.
They may make Hojlund look like a more solid #9 by taking some of the heat and being a bit more of a lightning rod for his markers, besides hopefully improving the delivery for whoever plays up front.
But Zirkzee, whatever you think of him, could be asked to stay up front a bit more, but not only will he not suddenly turn into a #9, it's probably a bad idea to ask him to throw away most of his assets. But it's also too simple to look at him, and then see his skills look to be something along the lines of ball control, dribble, build up/hold up and then stamp the guy a midfielder.
I do think that, if possible to do otherwise, it is not a smart move to put all your eggs into this what if scenario. We don't know how Cunha (and Mbeumo) will do, how this summer and more adaptation will aid Zirkzee's inclusion in general, and whether a false 9 or a direct poacher finisher 9 is the best companion to a successful new set of 10s. Especially since Amorim looks to prefer direct 9s like Gyokores and Hojlund, but the later games may suggest a warming up to Zirkzee up front.
I still believe in Zirkzee as a striker, but a Zirkzee type striker, not to transform him to a #9. If it looks like Amorim will only want him to be a real 10 or a real 9 (whatever that means), I hope everyone around him advices Zirkzee to find another team and manager. But Cunha and Mbeumo aren't exactly copies of the Sporting 10s, so I do feel like the current idea is to add a center midfielder next and maybe not a striker that will have to start for months before the plan is allowed to be deemed a failure.
I hope to see that front three of Cunha-Zirkzee-Mbeumo as theoretically they complement each other very well. But United has done a great job the past 12 years to show us that theory sucks and no player is reliable here.