I've spent some time with layout builder. Also by being SP Page Builder user for quite some time,
I've found that some features would be very handy here as well:
- Ability to clone items and rows. Add clone icon just before trash icon.
This would save a lot of clicks when creating more complex structure.
- Ability to collapse and expand rows, with option to remember expanded or collapsed state after saving.
This would save a lot of vertical scrolling and clicking when creating more complex structure.
Each row takes a lot of vertical space and collapsing finished rows would help to focus on current row.