The predictions of so called economists should be taken with a pinch of salt.
They are predicting up to 15 years ahead in some cases, who knows what state the world will be in next week never mind up to 15 years ahead.
Donald Trump could have a heart attack tomorrow and it would be blamed on the Chinese or Koreans or whoever,a world war could then ensue and that would be a boost for the economy.
There are any number of alternative scenarios that could play out ,so any computer generated predictions of the economic fallout from brexit are just that,
Astrology would be more reliable.