would have thought this is/was doable, even if not with out-the-box functionality then with some well established and well know plugins but tried searching but can’t seem to find the answer/solution.
(Coming from SharePoint where this is easily done, so this may be tainting our view a bit too much.)

We’re looking to setup a large site with many users and be able to group users and allocate permissions to sub sites (and sub-sub sites etc).
The most problematic part is restricting permissions for managing the navigation to within certain sections.
The SharePoint equivalent would be that if you are an editor for a subsite then you can create as many pages or subsites within/under that site (only) as you like.

We’ve looked at network sites which would appear to solve the issue of isolating permissions but this would seem to only allow for a single level of manageable permissions.

So, as an example scenario
We have Group1, Group2 and Group3
We’d want a structure something like
( Top/Network Site (Site 1) (Site 2 (Site 2A) (Site 2B) ) )
where Group1 have permissions to edit content and navigation(/structure) of Sites 2,2A and 2B
Group 2 have have permissions to edit content and navigation(/structure) of ‘Site 2A’ only
and Group 3 have have permissions to edit content and navigation(/structure) of ‘Site 2B’ only

there seem to be plenty plugins to manage permissions for content/folders but navigation/structure seem to be the sticking point.
It would appear to us that if we wanted Group 2 to be able to create/manage structure(/subsites) under ‘Site 2A’ they’d need permissions to edit the navigation of ‘Site 2’ which would give them the ability to edit the navigation/structure of ‘Site 2B’ which we don’t want.

So is the above achievable? Is it possible to restrict editing the navigation based on a (pseudo-)structure of the site?

Thanks