Apparently I should be using this as a guide to tanking on my Shadow. I'm gonna refer to this and use it often.
Especially Kirtu's part.
KN has some funky mathcraft in here, but the "catch all" is generally the best compromise between resource management and DPS+TPS. I'm a big proponent of KN's work on the gear/relic side of things, as they're black-and-white optimization questions. However, over-optimizing rotation can lead to the very real risk of encountering a situation you did not plan for and which breaks your model, so read and understand what KN is saying, but also recognize the caveats.
To my mind, the more automatic (and, by extension, less innately complex) your rotation is, the more attention you can focus on the battlefield around you to make more impactful play choices than tiny rotation optimizations. Voluntarily accepting a slightly sub-optimal rotation in exchange for simplicity is a worthwhile trade-off in my mind due to the mostly tolerant threat mechanics in this game.