It's the same whether you receive care at home or in an assisted living facility.
Even without such care, a lot of these people regularly need hospital care for things that aren't covid. Many have regular scheduled visits to doctors for blood pressure medication tweaks and similar. You could isolate the healthy 70 year olds quite well, but not the sick 80 year olds.
As you say you can expand the circle of isolation. All the at-risk patients (Say people over 65 and all adults with preexisting conditions). Then you isolate those people that they have to interact with. For example all staff at all nursing homes where any such person lives. But you quickly end up where you started. All the people who work in all the nursing homes have kids and spouses. They can't see those people when they aren't working, and then return to work with the risk group. They'd need to take their kids out of school for example (remember the point of all this is to make the rest of society work normally, schools are open). It's hard.
It's probably easier then to designate people as high risk "patients" and treat them with full protective clothing, move them to special homes where care can be given with more protection and so on. But that also requires 3 things: lots of staff, lots of protective gear, lots of time to set up. I don't think there is a surplus of any of those things. It might be something to consider for the long term.