By derestricting the amount that the local authorities can raise their council tax,

The possible rise in council taxes has not been 'derestricted', the cap on possible rises has been raised. There is still going to be a restriction of 5% (So council taxes will not even rise in line with inflation, without needing a referendum)
The fact that councils are permitted to charge more does not automatically mean that all council taxes will now rise to meet the new cap.