I say Joshua on points with a good margin or late stoppage. Ortiz was a great boxer but already in 2018 he was no longer young (39 years old but it is suspected that he was born before 1979), he had passed his prime and had lost something in speed. AJ instead in 2018 was in his prime and in full confidence, his speed and his good footwork in my opinion would have gotten the better of the southpaw stance, the power and the ability as a counterpuncher of the Cuban fighter. It's a shame that Ortiz did not go pro earlier, perhaps the history of the post-2000 heavyweights would have been different.
I'd go like 60/40 in favour of AJ. I think Ortiz was overrated by Wilder fans for obvious reasons, but still, he would have been a tough fight.
Speculation one way in one situation, and another way in another. What are these "motivational issues" we all know that Vladimir had? He showed up in top shape and tried everything to win (even throwing an intentional headbutt). Is this just you hoping? Ortiz fought a far better version of Andy than Joshua beat. Joshua lost to a short notice Ruiz who was "constantly training" despite not being in camp? Charles Martin's best win is a Gerald Washington who'd already been stopped by Wilder, Miller, and the fat Pole. Charles Martin, officially a "good, durable fighter".