In some ways I think the Tory campaign was the most realistic of the two. Clearly they've been preparing for Brexit and, despite appearances, are aware what a clusterfuck it's going to be. However, if you're wedded to the idea of carrying it out then you can't actually do any accurate economic forecasting or planning because literally who knows where the UK economy will be in March 2019?
I think they got stuck between a rock and a hard place - can't say Brexit will probably be shit, but can't cost any policies or offer any goodies because Brexit will probably be shit. So, let's use the poll lead to get a mandate for giving ourselves some flexibility (can the triple lock, wiggle room on raising taxes and VAT, try and address massive social care funding issue etc).
If they'd been a bit more intellectually honest with the electorate eg "we're in for a bumpy ride, we need some flexibility, trust us to be responsible", maybe they wouldn't have crashed so hard. I guess having talked up 52% as representing the will of the people they calculated that any rowing back on how great things are gonna be wouldn't have been too popular so "Brexit means Brexit means we can't talk about what a shitshow it'll probably be"
I hope this makes sense. Basically, if I was about to oversee Brexit negotiations I think I'd be looking to trim any onerous financial commitments to the public and I wouldn't be making any new ones if I could help it. I think that's my point!