It's interesting that you focus so narrowly on the example of Hollywood. There are quite easily understood historical explanations for how this dominance came about. Recall how for centuries Jews were systematically excluded from most professions. One which has always been open to them, however, is entertainment. Why? Because during this same period, it was disdained by the elite. In Europe and the USA, actors were long considered little better than prostitutes. (Many were
prostitutes, since it was often a more reliable source of income than acting.) Pogroms in Europe sent thousands of entertainers to the USA, where they concentrated themselves in urban areas and came to dominate vaudeville.
When the movie business was founded, it was marginal. Movies were considered a curiosity; like personal computers in the 70s, no one envisioned the world-spanning multibillion-dollar industry they would eventually become. The studios needed talent quick and they drew on the existing pool they had--the New York vaudeville scene. This was, as mentioned before, dominated by Jews so they were overrepresented among early performers and impressarios. The result was a sort of "founder effect". Jews were attracted to Hollywood because they knew they wouldn't face the same prejudices there as they did in other industries. So the original anomaly was reinforced.
So really, it was more dumb luck than anything. The Jews were prominent in an industry right at the time that it suddenly changed from something despised to something prestigious--and, ultimately, well-paid. Occupational specialisation among ethnic lines isn't unusual--examples abound from all parts of the world at all times. If running motels were to switch overnight from being something looked down upon to something vastly important, suddenly Gujeratis would become the most wealthy and influential group in this country. Not because of a longstanding systematic societal bias in their favour but because of a quirk of history which they are well-positioned to exploit.
Now that anti-Semitic prejudice is much less (although not gone completely), I would expect to see a reversion to the mean. What is the counterevidence? Instead of looking at what proportion of the "most powerful people in Hollywood" are Jews, you should look at the up-and-coming players. Are they still disproportionately Jewish and, if so, are there explanations which account for this beyond "they must be favouring their own"? (Compare the gender imbalance in STEM fields. The evidence is that it's small in grade school and grows over time [the so-called "leaky pipeline
effect]. Here the most likely explanation is a systematic bias against women, from societal enforcement of traditional gender stereotypes to outright professional discrimination.)
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons