I have two problems with the lower-arm-actuator-is-the-wrist interpretation.
-It means that designs like the JagerMech and Rifleman have art that don't match their stats. Now, obviously stats trump art and we're going to get inconsistencies no matter what, but the fact that anything with no LA/H actuators being able to flip their arms is a rule specifically of things like the Rifleman makes me want to assume they are correct and other things are inconsistent.
-There are lots of things that have lower arm actuators but no hand actuators, and I can't even comprehend what a wrist with no hand attached would even be. I'm talking about things like the original Warhammer, where the arm has two sections and flexes at the shoulder and elbow.
The interpretation I'm leaning toward is that the shoulder and upper arm actuators both move the 'Mech's "shoulder," but one controls abduction/adduction and the other controls flexion/extension. I think those are the right terms. Anyway, this suggests that the lower arm actuator is the elbow and art with elbows on Omnis PPCs/ACs is in error. It also implies MechWarrior Online is being dumb when it restricts horizontal movement on designs without lower arm actuators.