Latency when recording through aux to audio track

Routing from: One aux track with input from microphone

Routing to: One audio track with input from said aux track

Why on earth does this routing incur latency? Even in a clean session with no plug-ins, there is a 15ms delay (128 samples H/W buffer size).

The idea is to print plug-ins (e.g., Slate Virtual Microphones or low latency Auto Tune) and not have to instantiate 50+ copies across a vocal dub/backing session. Other DAWs do this with no added latency.

I have been googling this intensively, and there are posts going back to 2010 detailing this exact problem. Furthermore, all my Pro Tools and Pro Tools Ultimate colleagues have complained about this. Time to do something about it!