For these two I would call the examples you cite works of engineering instead of acts of magic.
But in TES, is there a difference? They use enchantments primarily, which are magical. They were the best enchanters.
Perhaps it's like with Vivec and Vehk, with the idea that Vehk killed Nerevar, but Vivec didn't. Mannimarco didn't achieve godhood; the King of Worms did, perhaps.
I honestly don't accept that idea yet, but I also haven't looked into it a whole lot either.
Vehk did and did not kill Nerevar. He split the timeline, so in one, he was always a god, and the other he was a mortal.
Manni probably did the same, kind of. When the Warp happened, we know that all the possibilities occured. So he became a god, but in the other realities, he did not. So part of him became a god, the Necromancer's Moon, and the other part stayed mortal, the King of Worms. So at the same time, there is the God of Worms and the King of Worms.