Was the 2017 election a good or a bad result for the Labour Party? As I write in this week’s magazine, that’s the question that now divides the party: as a majority of Labour is in the “good” camp, Jeremy Corbyn is in the ascendant, at least internally.

From a purely mathematical perspective, Labour gained both votes, and more importantly under the British electoral system, seats. Unlike after the 2015 election, which was such a bad defeat that realistically the Conservatives had won two elections in one night, Labour can plausibly expect to win power at the next election. There are more than enough seats in the reach of what, by historical standards, would be a below-average swing for a party that has already lost three elections in succession.

So, progress. But from a political perspective, what if 8 June was “peak Corbyn”? What if this is as good as it gets? As you’d expect, how an MP feels about this argument tends to be a pretty good guide as to how they feel about Corbyn.

But the oddity is that the opinions really should be the other way. You can make a strong data-driven case that Labour’s 2017 election result was about Corbyn – that the party advanced in exactly the places that were rich with the type of voters that even the largely disappointing 2016 local election results, and the astonishingly bad 2017 local contests, showed Corbyn was adding to Labour’s appeal with. Labour made amazing gains anywhere that ethnic minorities, social liberals, graduates and the young clustered in significant numbers. It did less well, and actually lost some seats in places that were ethnically homogenous, socially conservative, and older and/or less well-educated than the average.

Corbyn has always been less unpopular with ethnic minorities, social liberals, graduates and the young, and in many cases quite well-liked – he is now very popular with these demographics. So that’s the case for “It’s Jez wot done it”.

The difficulty if you accept that case is that Labour is near to “peak metropolitan” as far as its potential to add more seats at Westminster goes. There are a few places – Putney is one, Cities of London and Westminster is another – that could be gained through adding more of the same types of voters to its tally. And Labour actually could probably get a small parliamentary majority or a stable minority government with that approach: a swathe of gains from the SNP in Scotland, plus the likes of the Swindon seats, could get Labour close to or slightly above the magical 325 number without changing the demographic make-up of its 2017 coalition all that much.

But if you think the election result was in spite of Corbyn then why should the gains stop at 263 seats? Why not 325? Why not 400? You can make a good case that Labour’s gains came because of May, not as a result of Corbyn: the 2017 local elections showed what an excellent position Theresa May had at the start of the campaign, and the 2017 general election was really just the result of her squandering that advantage.

The thing is, though, that if Corbyn can take at least some votes by default, at that point, you can’t really argue that he can’t take lots and lots of votes by default. That was the argument that people made when they said that Labour’s leader was “unelectable” – that no matter what, his Labour would be so voter-repellent that the Tories would win by default. What the 2017 result showed, at the absolute worst for Labour, was that the limit does not exist: the Opposition can take votes from the government by default.

Bear in mind the fact we are looking at the prospect of a sharp and traumatic exit from the European Union and an economy that is, in any case, due another recession before the next election. And at that point, no matter what you think about the Labour leader’s ability to actively attract voters, the question, given that the least complimentary thing you can say about Corbyn is that he cannot repel voters, is: why wouldn’t he do better next time?