Two calls wouldn’t be necessary if this feature was added: NNS Governance canister feature request: list_neurons by subaccount
Clients can compute their own neuron subaccounts, like principal + nonce, nonce can be a simple incrementing number and you can easily query certain neurons if list_neurons supported subaccounts like all the other endpoints do.
There could be a new method list_neurons_by_id_or_subaccount or there could be an optional value in the current list_neurons method like neuron_ids_or_subaccounts.
Maybe the team can look at adding this too since work is being planned here.