He was never right last year health wise.
He impressed this Spring. He's apparently been impressing this Summer.
I believe if he looks strong next Spring, and performs over the first two months at AAA.... he'll be up for good by Memorial Day.
One of the big unknowns in the O's system this year is what Diaz would've done with a healthy full season. As you noted, he's reportedly looked good at the alternate training site, so I'm hopeful that he's in a good position to perform well with better health in 2021.