Anyone wishing for HS2 to be cancelled need to provide the answer to the question of the extra passengers which are using the WCML compared to the predictions.
London to NW sure have been ~10 million trips per year at the opening of Phase 2a yet in 2018 it was ~11 million. If you compare 2018 actually & 2018 predicted the numbers are much more stark. 2018 actual ~11 million 2018 predicted ~ 8 million, so about 3 million extra passengers (or getting on for 50% more than expected).
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That's just on 1 of the flows which would benefit from HS2.
With the extra services proposed by First on the ICWC franchise it's likely that growth will continue.
This sort of data is that which the review will be aware of and without an argument against it those opposed to HS2 aren't going to get very far in HS2 being cancelled. Even with higher costs, as there's extra people using the services.
It's also why the likes of Coventry aren't going to see the decimation of its rail services (not that it ever was, just that the model assumed 1/3 IC services and said nothing about the existing non IC services).