As far as I can see anybody ordering a car after October the 1st will only receive £250 GCP instead of the £600 GCB for a 3year lease. Or am I reading it wrong.
No, your are reading it correctly.
In effect a net cut of £350 to the GCB for cars ordered on or after 1st October 2022.
Motability have somewhat mudded the issue by paying existing customers £350 before their lease end and then only receive £250 at lease end (to align it with the new payment for post 1st October 2022 leases).