Running around on the sideline is not the only way to show leadership. At the same time, I have no idea if Watson was doing that or not because they are not covering the sideline every play. The media goes to what fans seek and at the moment that means looking to seeing what KC, a legit contender, and Mahomes was doing so the camera favored their sideline as to be expected.
Either way, if the team accepts and appreciate Watson's style of motivating and play then that's all that is needed. I've seen QB's that run around doing the ranting on the sideline or such and I have seen the more casual. Both styles have success to a degree but in the end these are grown men and professional athletes. If there is no self-motivation then there's a problem.
This is the last thing I think we should even worry about. Speculation and wonder when we don't see the sideline every play, when we aren't in the locker room, etc., is pointless. It's too much assuming spent. I question more the playcalling when we all know we should have a moving pocket, should see more runs on the edge especially with the likes of a Duke Johnson, Watson and such instead of seeing Hyde up the gut. I question more why we don't do no huddle when every time we do it we seem to have more success. Those are more of a concern.