As with Swindon, I think York's strong London service is due to its place on the network as much as to do with demand to it. Without a faster route between Sheffield and Leeds, a Liverpool Lime Street High Level – Prestatyn tunnel, reinstatement of a north-south route through Nottingham or massive works around Castlefield, those cities aren't going to have the same level of demand for through services as York.
I think the current / planned for this December levels of London services are as far as it should go for now. If HS2 had been going ahead in full, I think 4-5 tph for London – York would have been justifiable (2 tph HS2, 1 tph via Peterborough, Newark and Doncaster, 1 tph via smaller ECML stations plus Grand Central), but without it, other services should be prioritised even considering how much rail demand to / from London compared to other cities there often is.