Your understanding is... well, interestingly wrong. That ("they never intended to leave the common market but to gain a trade deal that would leave market access substantially the same") _was_ the narrative pushed by the yes-for-brexit campaign, by and large, but expert opinion from the start was that this was not possible. The UK wanted to have full access to the common market (except for labour) but without following European laws. This was obviously, from the start, ridiculous positioning.

> However, the EU wouldn’t let them keep access in the divorce if for no reason other than as a cautionary tale for other member states.

How would you propose that this access would work, given that the UK refused to accept EU regulation?