They ASKED Zeno to become sole emperor, and Zeno told them to stuff it, which they did.
BY ASKING Zeno to become the sole emperor, the formal roman power in West renounced territorial collegiality, which is the only thing on which the historiographical definition of WRE (and there's not one contemporary definition you could find) and therefore making WRE going down.
It might be surprising, but historiography of ancient polities have actually few to do with discussion on defloration or rape.
But the thing is THE SENATE ACCEPTED NEPOS (against their initial wish, sure, but they accepted him nonetheless)
Sure,
IT DID ACCEPTED NEPOS, but not on the grounds of territorial collegiality.
First, Odoacer revieved the title of Patrice, and governorate of Italy, from Zeno and not Nepos. That alone points that Nepos' power was de facto bypassed by Zeno, intervening directly in Western politics, breaking territorial collegiality.
Then, the lip service to Nepos isn't much different from the lip service Romans emperors recieved from, say, Burgundians or Goths. So far, nobody argued they were part of Byzantium for that.
Even the lip service to Nepos wasn't without breachs :
coinage made, even during Nepos' reign, often rather bear mentions of Zeno.
Finally, having the Senate directly answering to Odoacer and not a Roman Emperor in the west, pose an important question about how the West percieved Nepos' power : arguing that
THEY ACCEPTED NEPOS as emperor in the West, in a total continuity should be at the very least nuanced.