It isn't a plothole if it didn't work...
Technically it is actually.
Kabuto directly described the fact that after the summoning is successful, the caster can confine the edo in a coffin and prepare them to be summoned later. The fact that Oro summoned Minato just like he and Kabuto summoned everyone else would mean that the summoning was initially successful. If he did actually try to summon Minato, the summoning would have initially failed and he would never have had him ready in a coffin. Now the coffin was actually never shown in the manga, but since he was attempting the summoning, its strongly implied that Oro had a coffin ready.
I hope you understand my point but yes, Kishi made it clear that it failed because Minato is sealed in the deathgod already, but technically it is a plothole based on how Kabuto described the pre-preparation process.
