The FT says Reeves’s outrage at the state of the public finances was “justified” but “planned in advance”:
You cannot fault the politics. As Rachel Reeves denounced the largely predicted but still shocking black hole at the heart of the UK’s finances, you had to respect the chancellor’s craft
… while Reeves may have been shocked by the detail of the public finances, and her outrage at Tory mismanagement wholly justified, her performance was largely planned in advance. The broad fiscal picture was known before the election. This was all part of a political strategy to temper public expectations, affix blame to the Conservatives and instil patience in her own MPs. It is also likely that the tax rises she implied were unnecessary during the election, but will announce in October, have long been known to her.
So yes, those of us who fixate on the machinations of modern politics can appreciate a game well played.