What problem does this address?

The Inner blocks use content width toggle has always been confusing to our users. They expect content within containers to behave the same as content within the top level of the editor. This was solved with is-layout-constrained, but it seems that there are still varying defaults on different blocks.

Our biggest issue is the column block, which still defaults to is-layout-flow. A Columns block with a single Column block in it has the opposite default to a Group block (the two being otherwise mostly indistinguishable from one another).

What is your proposed solution?

All container blocks that support layout should be set to is-layout-constrained by default. I want to be able to turn off the layout controls now that that's an option in theme.json via settings.layout.allowEditing, but can't because the Column block still defaults to the wrong layout.

Further, letting us define which layout gets used by default for all container blocks in theme.json (and then further customizable on a block-by-block basis) would be even better.