Every coin has two sides.
The core of your belief appears to me to be that Johnson is aiming for no deal. I think he wants a deal.
The aim of the 21 MPs you refer to is either to remain or that they have the view that a decent deal can be obtained by consent of the EU and without the threat of no deal.
My view is that the EU have demonstrated that they wish to shackle us into a subservient deal and they are not in any way benevolent.
I believe that the only way we can get a fair deal out of the EU is if they genuinely believe that they have something to lose. Consequently, we have to make them believe that we are prepared to walk away to force them to renegotiate. Validity of that view has been proven by the change in stance from the EU since Johnson came to be PM. Historically, they repeated the mantra that the deal couldn't be changed. A few weeks or the real risk of no deal and now a chink has appeared in their armour and they are discussing a renegotiation.
I believe that that Johnson does want and deal and is following the strategy described above. Yet he has no majority and there is a body of resistance in Parliament that is determined to wreck and undermine this strategy to either keep the UK in the EU or weaken our negotiating position to the point that we accept a deal that is almost the same as remaining in the EU.
With that in mind, I believe that Johnson is using whatever tools he can, including prorogation, to attempt to stymie the wreckers.
I do not think he lied about prorogation and i do not think he's lied about negotiating.
I also think that if we cannot get a deal out of the EU before Brexit and we leave with no deal, a deal will be forthcoming fairly quickly afterwards. Yet we may have to risk leaving with no deal for that to be the case.