Stack of smart groups within smart groups within Parent groups

I've seen several customers stacking up smart groups within smart groups within Parent Groups and then also removing contacts from the smart and parent groups directly and then do a Mailing to that Parent Group.

At a certain level the Mailing fails (one example: resulting Parent Group had 130K contacts), with unclear error messages like
"A fatal error was triggered: is not of the type Integer"

I am not sure what the best answer would be.
Maybe at least be warned that stacking up smart en parent groups is not always a good idea.
And a better error message when CiviCRM fails in creating the resulting Mailing group.