However, in respect of getting a quick U.K.-USA trade deal in place there is no doubt he would have been better for the U.K....
A quick one? Maybe. A good one, definitely not. If I'm negotiating with someone, I would want them to be a fairly reasonable, stable individual who can weigh up the various parts of a proposition, realises they have to give quarter and can be relied upon to stick to it when the deal is made. I think you just thought Trump was the best option solely because he's described as "right-wing" and maybe reminds you of the numpty Prime Minister you worship. But dealing with him would have been a disaster. Your deal with the EU isn't great, so you need the US. You don't want to be banking on a guy who believes in Qanon and is only happy to incite an insurrection in his own country because he didn't get his way. Cutting a deal with such a man wouldn't be worth the paper it was written on