I prefer to take vertical space than horizontal because vertical scroll is more common to users than horizontal.
The main goal is to show that there is something.
When looking at a sale order, it is good to know there are complaints or that there are two shipments etc. This allows the user to have a quick picture of what is going on (or not going on).
Relate buttons are more an advanced features. We see often that users ask question on how to find something which is in a relate but they do not know because they do not see it.
Well we display on the form the most important one for discoverability and quick view.
Well almost nothing is duplicated because we reuse the existing actions.
See:
Also it will make the display of the drop-down very slow compare to the current implementation that use a cache on the record. (menu actions are not form related as they are also on list/tree).
That’s why we keep the relate.
As usual option is the non-answer. We need to have something that works for everyone.
Also this feature is the first step to Include dashboard in base module, we can not make them optional otherwise dashboard will be pointless.
They are displayed in a group so developer can activate the expandable feature. But it will probably requires to have a feature to remember the user choice.