My thought about this was to shield the vulnerable group until potentially April/May- where lockdown would be longer for this age group. Prioritise all home deliveries from supermarkets and pharmacies to this age group so they don't need to go outside until the under 70s complete the vaccination programme unless an over 70 is in a support bubble with under 70s or has a business that needs to work or has a health condition that requires frequent hospital visits. In the meantime, get everyone vaccinated that are under 70 so that we can open up instead of all of us being in lockdown potentially until Easter.
But you're still not thinking of the reason businesses are shut etc.
It's not because people in general are catching it. It's not to stop staff "dropping like flies" and making places short-staffed.
It's because when anyone extremely vulnerable to it catches it, they disproportionately end up in hospital. Overwhelming the system.
You can't "shield" the ECV and the over 70s effectively. They're not cut off from society. They catch it - from carers, from their family members and so on - and then they end up in hospital overburdening the NHS. You said it yourself:
unless an over 70 is in a support bubble with under 70s or has a business that needs to work or has a health condition that requires frequent hospital visits
That's absolutely LOADS of people. The majority, probably.
So we need to vaccinate them all first. It's the only way. You and me getting a vaccine won't help businesses open up. The vaccine doesn't stop you transmitting it. It just reduces the severity of the symptoms if you catch it.