First, I'll note that clearly Tiafoe is a level below Med to begin with, so just at a base level, the result isn't surprising at all.
I think Foe's problem is that he's trying to out-Med Med and he can't. And if you think about it, that's sort of how Tiafoe plays - minus the massive consistency. He has a serve that can do damage, he likes to cat-and-mouse, he goes big sometimes, but not all the time. But it's all at a level below med. He can't stay in rallies long enough to challenge Med and draw a lot of errors.
So what to do? I'd say go higher risk - go bigger than normal. Total aggression, a la Sinner, really isn't really Tiafoe's game either. He's sort of between an outright aggressive game like Sinner and an extremely measured game like Med. But in this instance, where he's never going to win playing extremely measured - I'd say just go bigger. Bigger first serves, second serves, a little bit more urgency on big groundies, and still, of course, work in net play and drop shots if there's an opportunity.
If he does this and makes a ton of errors, people will call him out for for looking sloppy and irresponsible. But the starting point is that he's the underdog to begin with, that Med's the better player, and he can't out-Med med by playing 15 positioning shots before winning the point. So, playing outside of himself is somewhat necessary unless for some reason Med is extremely off and missing a ton early - which he isn't.