Yep! You're basically building a custom _all field which includes the denormalized values of the children too. There used to be a include_in_root option which would do exactly this, but it was removed since the same can be done (more generically) with copy_to.
That's pretty much the only solution in this case, regardless of version... nothing new to help out. Relational support in ES is fairly limited, since it can only consider one document at a time, you need to do these kinds of tricks. 