The hymns addressed to the all-gods invoke Indra, Agni, Mitra and Varuna by name in the same breath, which is difficult on the totality reading and unremarkable on the class reading. The ritual tradition then gives the Vishvadevas a portion of their own in the domestic and ancestral rites, which favours a class, but ritual is capable of serving a formula a plate.
What would resolve this A systematic account of what the hymns addressed to the Vishvadevas actually say about them, set against the hymns addressed to named collectives such as the Adityas and the Rudras, to establish whether the group has a describable collective character or only a name.
OpenVedic philology and the study of Vedic ritualArthur Anthony Macdonell, Vedic Mythology