(Labour.)
And of course, making Labour viable is the over-riding criteria against which Corbyn should be judged. Succeed at that then all his other failings can be overlooked to an extent. Fail, and he's got to go, and that judgement will be made in 4 weeks time.
That rather depends on the what the long term objectives of the party are. If the objective of the party is to be a party capable of forming a government or being the senior party in a coalition then IMO you are absolutely correct.
OTOH, if the objective is to recast the Labour Party as an ideologically pure 1970's style Socialist party and then hope that either they will be able to persuade the electorate that they should vote Labour or that, as a result of the policies of four decades of "right wing" Conservative, Blairite and coalition governments, the electorate will decide that they need 1970's style Socialism then establishing and adhering to a new ideological purity is the key criterion against which he should be judged.
I personally think the Labour Party should be doing the former, the majority of the current Labour Party membership seem to be doing the latter.