I think Romanov, Plechko(If his chin is strong?), Kuzmin(He had a close 9/7 loss to Joshua in amateurs), Ali Eren Demirezen, Ortiz, Browne, Oscar Rivas, Joe Joyce, Hrgovic, Andy Ruiz Jr, Tyrone Spong, Simon Kean and Haye if healthy, all can compete. Your list?
You know a lot more than me about HW's houmzz but you got Andy Ruiz but not Joe Parker. Why is that ? Daniel Dubois ?
Ruiz beat Parker in my view.Also, has more head movement and is a little bit more powerful.Dubois is untested, got stunned by Mendouso in his 2 pro fights.And Dubois gets hit a lot, much more than Joshua.
With the exception of Ortiz, Joshua would currently walk through that list pretty easily. And he beats Ortiz too, but with some difficulty. Parker, Povetkin and Wlad should be added to Ortiz to complete a credible list.
Except from Ortiz, no other boxer from your list stands a chance at this moment. Klitschko, Povetkin and Ortiz all have a good chance to beat them. Mike Perez, David Haye and Tyson Fury would have a good chance as well if they are in good shape and 100% fit
Of the current top 10. Wlad Povetkin Ortiz Wilder Parker All have a 50/50, 60/40% chance with AJ. Joshua is very good but I don't see thus unbeatable force alot of people see.
Wlad, Wilder and Ortiz are the only real threats to Joshua right now. Some of these prospects might be competitive in the future but right now, no way.
None of them can compete the HW division is Fury and Joshua The rest are old, too small, drug cheats or just complete stiff idiots.
Wilder and Ortiz both beat Joshua and if Fury ever comes back he would also. Parker and Browne could compete, but Joshua beats both of them. Povetkin could be a threat with the right gameplane. I also think Joshua came in too heavy in his fight with Wlad. If he came in about 10 pounds lighter he would've ended Wlad earlier. He clearly gassed midfight against Wlad and needed a few rounds to get a second wind. I could see all the above fighters using Joshua's poor stamina against him and getting a stoppage win over him, since he showed that same gassing problem with Whyte, who nothing special.
I can easily see Wilder Sandersing Joshua. If Wilder drops Joshua like Wlad there's no way he can take a few rounds off to recover. Wilder will finish him. Nobody is lining up to fight Wilder because he has fight ending power.