@nurgelrot I will be sure to post as soon as I find out! You are correct about the starvation on the Pi side when it comes to a Pi 4 as the power requirements (for the Pi) are somewhere in the ballpark of 5A whereas the Duet is only able to supply 3A max on top of any other peripherals that require a 5v source. The symptoms usually show up as a warning on the Pi.
I have also read about solutions where the SBC can power the mainboard but something about it just feels wrong, also since that LRS-100-5 can supply up to 18A, I figure why not use it to also supply the duet.
I figured with all of the people on this thread it should have been a slam dunk to get an answer by now. I will post my findings if I decide to give it a go on my own. Hopefully I don't cook any boards haha