Your loyalty is to doing your job to the best of your ability and trying to improve as much as is realistic, assuming all other things being equal by which I summarily mean you don't work in a toxic place.

As for RSU's, as others have mentioned, it is great to think of it as additional money and base everything on your base pay (pun unitended). Never sign up for a job where your base pay may vary based on RSU grants, I am surprised to read something to that effect on this thread.

As for job security, I don't think it is a function of your role, salary base pay or stock grants. It is a function of market dynamics and how your company is doing well in the space it operates in, so it is our job to keep an eye on that. If you see winds of change that may hurt you, one better ensure not getting caught in the crossfire.

So I think it is better to be loyal to your own career and the good side effect of that is being loyal to your role and hence your current employer!