"If you notice, the claims of Brexit supporters since the referendum have slowly morphed from “ we’ll get a great deal and be better off” more or less to “the sky won’t fall in and at least we can do our own trade deals”"
There is an element of truth there. At the start most assumed that the EU would be represented by decent, responsible individuals looking to do the best for the EU members. It took a while to realise that their lust for power in Europe overwrote that.
But long term we will be better off, but we have to make the first step and deal with it. Unfortunately parliament, aided and abetted by the EU, is trying to avoid that.
I doubt any leaver is suggesting "at least" something. That's remainer speak. The points are that remainer doom and gloom, worst case scenario claims are unaccepted, but there is the agreement that any change initially brings disruption and issues. But good management sees us through that. And afterwards we will have regained sovereignty and world wide trade deals with nations, and likely exceed our past achievements.
The referendum wasn't flawed, it was a simple question which was answered, yet still to be fulfilled.
Brexit will end on the date we leave. Rebuilding given the new situation will take longer, but the incentive is there. This is what was voted for.