It was in Vote Leave adverts, though admittedly they made the promises separately. For example, we'd "take control of our borders and put an end to free movement" but also "retain the right live and work in the EU."
Led by Donkey's has been really good at compiling quotes from the Leave campaigners saying stuff like "There will be no downsides to Brexit. Only considerable upsides" or that "the day after we leave, we hold all the cards and will be able to choose the path we want".
At the risk of sounding elitist, I think you might be over-estimating a lot of the voting public. The day after the Scottish Independence Referendum, a guy I worked with came in all excited about getting DevoMax. Because Gordon Brown said so. Nice guy but he had very little interest in politics and just believed what he saw on TV.
You might not consider Boris Johnson, Michael Gove or David Davis "serious, well regarded politicians" but a lot of people do, even now. And a lot of people took them literally. That's why they won.
Is No Deal really much of a threat though?
"Give us what we want or we'll destroy our own economy!" really isn't much of a negotiating strategy. I mean, no deal will hurt the EU but nowhere near as much as it'll hurt us. Even if it was, it's effectiveness is pretty much fucked considering Johnson is openly telling the media that it's a bluff.
Are the EU even dictating terms? From what I can tell, the Withdrawal Agreement was May's attempt at satisfying all the different groups in her Government. The backstop, for example, is pretty much the only way to avoid a hard border in Northern Ireland (which no one wants) without a border in the Irish Sea (which the DUP don't want) or retaining free movement across the UK (which loads of people don't want). The EU appear to be just going "Fucking hell, what do you actually want?!"
Nah. I'm not having this.
From the moment the result was announced, the Tory Party closed ranks and refused to let anybody else have an input. I believe that she even tried to block Parliament from being able to vote on it! It's hardly the fault of the SNP, Labour or the Lib Dems that the Tories couldn't decide what they wanted from Brexit. It was only after May lost her majority and couldn't get her deal through Parliament that she started reaching out to the opposition parties. Not for input, just to rubber stamp her deal.
There's a lot of criticism to go around - Labour's lack of a position, and the Lib Dems recent "revoke" strategy for example - but the absolute bulk of the blame is on the Tories.