Oh wow, it turns out you are right. Great, I'll definitely be doing this!
My only regret is that you evidently can only do this once (for instance, you can't seem to have three layers of track stacks at once). Correct me if I'm wrong on that one.
Apart from later adding the ability to have more than two layers, hopefully we can do this with summing tracks as well.
But apart from that, thank you for pointing this out! Now that you've mentioned it, the action seems so simple.
Logic Pro 10.5.1
Software: OS X 10.14.6
Mac Pro (Late 2013)
Processor: 2.7 GHz 12-Core Intel Xeon ES
Memory: 64 GB 1866 MHz DDR3
Graphics: ATI Radeon HD 5770 1024 MB