Going to make somethings clear.
Machia's stamina of 48+ Hours comes from his "fight" against the LoV. The gap between them and Machia is greater than the gap between an ant and a human. While this is still impressive, we have zero reason to assume Machia can fight at 100% for this long.
Note: Humans can walk for around seven hours or more, with no breaks. While we can only sprint for around half a minute before slowing down. Obviously, I'm not saying this is how the fight works here. I'm just using that as an example, that Machia's ability to fight at 100% should not be comparable to his 48+ Hour feat.
He was dealing with people who were vastly inferior to him and it was even revealed he was holding back the entire time. Stamina alone is only half the battle as well, since Machia will be taking damage from Dark Shadow's attacks. Lets say he can move at 100% for 24 hours, who to say he can do that while taking damage as well?
Machia's ability to fight on while ignoring damage is unknown due to the fact the only time he was really injured, he was killed in one hit. Damage accumulates and Machia cannot heal, he just ignores it. But a broken bone is a broken bone, and Machia is going to just be tanking a barrage of attacks from Dark Shadow.
Who's actually noticeably bigger than Machia. Note: Machia is in the foreground while Dark Shadow is in the background.
Not only that but Dark Shadow can fly and extend their limbs beyond the normal length.
And while they scale to the same value, I do believe Dark Shadow is stronger.
Dark Shadow overpowered Rewind/Prime All For One, who only escaped by exploiting Dark Shadow's weakness to light. While
Machia's attack didn't even seem to damage a less durable All For One.
Also, damaging Dark Shadow doesn't do anything to Tokoyami. While Tokoyami does tire out while fighting, any attacks on Dark Shadow itself does nothing. Which isn't true for Machia who does take damage, he just ignores it, which doesn't change the fact he's being hurt and that will accumulate.
Note: I don't believe it's wrong to say Machia will outlast Tokoyami, we know for a fact he does get tired while fighting all out. But I want to make it clear the fight is far more complicated than just, Machia outlast him and there's nothing Dark Shadow can do. When he's damaging and breaking Machia's body.
There's a far bigger difference between walking, running, and running while you're being attacked by someone on par with you.