1tisILeClerc
Those reports are 'old data', December 2018 one of them and 2016 for the other.
The George Osborne link is from 2016 of course - the same month and year as your George Osborne link. 
we have to sign the WA to negotiate a deal with the EU
Not signing the WA cuts out the 21 month transition period - we won't have to adopt new EU rules and regulations we don't like, particularly on matters that do not affect trade in goods with the EU.
Trade with the EU won't stop with 'no deal'- it will just be on different terms until/if we agree a free trade deal. It may be that we end up signing a series of mini deals with the EU - bilateral trade agreements similar to the ones we have with other countries around the world.
I think Barnier said there had to be a 'solution' to the Irish border, that's not the same as signing the WA.
That means that if by some miracle we find some competent negotiators and manage a better deal with one of these countries than the EU have, they have to offer the same terms to the EU.
I don't think you are right with this statement (I'm prepared to be told otherwise) - the WTO website suggests we can make our own trade deals (with non-EU countries);
"The ever-growing number of regional trade agreements and preferential trade arrangements is a prominent feature of international trade.WTO members participating in these agreements are encouraged to notify the WTO when new agreements are formed."
www.wto.org/english/tratop_e/region_e/rta_pta_e.htm
Revoke = problem solved
Until the next General Election when the Brexit Party take a third of the seats in Parliament.