When you have a dependency chain like this:

  initial --[data dep]--> group --[dep]--> final

Should "final" be considered a data dep of "initial". Currently GN says no. Groups are not special in any way as far as deps are concerned, and if the group was a shared library, it would be clear that the deps would be linked in to the shared library and not be considered data deps themselves.

However, this goes against the common usage of groups which is to forward or expand to a list of things.

Executables already have a special behavior, because shared libraries they depend on will be data deps if the executable is a data dep itself, and will not be considered at all if the executable is a regular dependency.