The tautological definition is, I think, better than making the mistake of confusing something like effort with work. A CEO does not exert 200 times more effort on the job than an average employee. How else can we define work to explain how technology enables people to "do more" today than before?But it is certainly not impossible for a CEO to make 200x as much difference to a company's revenues as the average employee.
Well, a tautological definition of anything will always be superior to an incorrect one. In the former case we learn nothing but are no worse for wear, and in the latter we may be acting on bad information. I'm not sure a new definition of work is needed. Some work requires less physical exertion and some requires more. Some work is quite valuable and some isn't. These parameters may or may not intersect.
I think you have the dictionary on your side. I also take your side in believing that the Facebook CEO has done a lot of work. When mk says "organize communication" and "create an efficient organization" that sounds like work to me. If we measure who is "productive in terms of work performed" by "who would have cost the business the most if they had never gone to the office" it's possible that MZ's income understates his contribution.