The first thing McSweeney should have known in his job was that the government would be viciously and crazily attacked by the right wing press from the moment they were elected (and obviously before they were the government).
The second thing McSweeney should have known was they would also be viciously and crazily attacked by the Corbyn era MPs and their cabal.
Basic stuff that, say, Alastair Campbell would have had known instinctively.
Of course the government has complicated things further by u-turning frequently and not shouting from the rooftops the things they have improved.
I also think it was a major mistake to lead with an unashamedly "it's going to get worse before it gets better" narrative from day 1.
Still, it's taken the spotlight off Rachel Reeves for a bit all this.