Tony Stark can defeat The Hulk in the Hulkbuster, but how can he fare against a “hulk” covered in bony, spiked armor of his own…and come back from the dead immune to what killed him?
No.
If your opponent has the power to come back from the dead immune to what killed him, that just means that you need to incapacitate him without killing him.
Tony could just call Thor and have him use one of Mjolnir’s portals to transport Doomsday to Hela’s dimension or somewhere else he couldn’t do any harm.
A sort of “phantom zone”, if you will.
Doomsday was pretty unstoppable. He would’ve defeated the hulkbuster armor.