Answering my own question here, but did some additional research and overlooked something which I had already checked previously.
Big shout out to @tcrs_circuit who I can tell has done a lot of work documenting his findings about this board (checkout https://repair.wiki/w/A2442_2021_14%22_MacBook_Pro for a ton of good info). But this machine will not power on without the battery connected on USB C alone. It ***needs*** MagSafe 3 input in order to boot when the battery is disconnected. Which makes me much less confused about why this machine is not turning on.