Saw your original request and the boneheaded response you got.
It’s honestly baffling.
And no, using a render target doesn’t look quite as nice as properly composting the buffers.
Otherwise everyone would just do that, since you can use sprites too the cost would be miniscule if only one could get it to look any good…
Also.
It’s not really a “cheap hack”.
It’s how games were, STILL ARE, and still should be actually made.
Just because one developer considers it a hack - without actually having any idea of what he’s even talking about - doesn’t mean it’s an actual hack…
What is a hack, is hacking the rendering pipeline to overlay a render target… though maybe I should pull the source and try that 
(The reasoning behind It being you have total granular control of all of the layers of both scenes, and modifying the pipeline is probably a faster result for composting when done properly. Normal with normal, roughness with roughness, etc).