Marvel time machines don't actually do anything useful, do they? I'm pretty sure that using a time machine in the Marvel U just gives you holodeck adventures.

That said, given that his origin is "used a machine to open a gate to Hell" I tend to assume that Doom just always uses magic and technology together when he feels like it. He used magic to see the future, but that doesn't mean it wasn't as a component in his Time-Viewing Omnicomputer.

I agree that the T'challa thing was just for illustration for the Panther God's sake. This isn't undermining "Rule the world, stomp down Richards" - it's just giving what the author believes is the reason he is motivated to do these things.