There are other factors also.
A privately owned house with a sitting (regulated - cannot be evicted tenant) tenant, may typically worth just a third of a property of what a house with a modern assured shorthold tenancy would be worth.
This reflects the value of security of tenure. A council tenant acquires security of tenure. He has the right to leave at any time, but unlike a private tenant he cannot be evicted at the whim of a landlord.
Further, if you have a council tenancy then in the event of the council wishing to redevelop its land, you will be rehoused on a similarly secure basis. In the private sector if the landlord decides to knock your house down, then you may have just a month's notice, and it's tough shit.
The fact is that it is not reasonable to compare a council rent with the rent for the same house on the private rental market (and in many cases due to right to buy, you can get houses on the same estate on the private market), because in reality the fair market value of council rental is HIGHER than the equivalent, assured shorthold tenancy, turf-you-out-on-a-whim private tenancy. Secure tenancy is a massive deal.
The right to buy is another factor. This is a discount of up to 70% on the market value of your house. This is another subsidy accruing to council housing, and worth up to £100,000. As an example, if you stayed in a council flat for 5 years, you might pay £400 per month in rent, times 60 = £24,000. If you then exercised your right to buy, you would receive a £100,000 discount from the council, based on a council flat in London worth £200,000.
If the market rent for the same property is £600 per month, then a private rental sector tenant pays in the same time £36,000, as against negative £76,000 for the council tenant.
The difference between the two hypothetical tenants, one private and one public sector, is £112,000. One tenant is £36,000 worse off than when he started, the other £76,000 better off. For HA the discount, under Right to Acquire is 'only' up to £16,000.
Clearly it is utterly ridiculous to suggest that there is no subsidy to council/HA properties.