Abby Normal wrote

When it is sized to the load the problem is it would only shut off for
an hour or two as the house cooled, then it would run steady until
after the sun came up to catch up. No real point in setting back.

That is just plain wrong. The whole point of a set back is that
less is pumped at the setback temp because the losses are lower.
How much lower depends on how well insulated the house is.

The only way set back works with a heat pump is if it is grossly oversized.

Wrong again.

All that accomplishes is set back without auxiliary heat.
It would short cycle inefficiently except for when it was
trying to recover from a set back.

Not if you one of the systems sized so that doesnt happen.

In an environment with an ambient dewpoint above 60F there will
be problems with a grossly oversized system in cooling mode.

Again, not if you have more than one system.