but the U.K. has never wielded less power on the world stage"
You (and Haaretz) could be right. But that is the position that he finds himself in, following on from Theresa May. Whether he will be able to turn that position around, or will allow it to deteriorate, is another matter, and remains to be seen.

That does sound rather like an attempt to blame Teresa May for everything that may go wrong. But it is certainly not the case for Brexit, because we have heard many times "Nothing is agreed until everything is agreed." So if there is an agreement, it will be Johnson who agrees to it, however much May was involved in drafting it. It is his responsibility for whatever arises from any deal he accepts. not hers.

No deal is marginally less clear, because part of the problems that "may" arise (to use Nigel's formulation) are due to our being woefully under prepared. May does take some blame for this, but since Boris Johnson assures yet again how low the level of pain will be, he would not be able to blame her for lack of preparation with any credibility, in my opinion.