You absolutely CAN judge the profitability of a movie comparing production cost to theater revenue. In fact that’s the ONLY POSSIBLE WAY to judge it. Yes there’s all kind of weird accounting that goes on around it and also have the marketing, and no actually the theater don’t usually get a large piece of the revenue (standard distribution contract that the theater gets 20% of the first week, their percentage slides up over the weeks, but by the time they get a large percentage the movie has bled out and is making nothing). But in the end there’s only a few numbers we know for sure:
production budget
revenue
And if the first weekend’s revenue is twice the production budget that is a successful movie, period.
20% is a large piece of gross revenue compared to the standard net actually received by many distributors, like bookstores, of other “creative” activities. A former colleague of mine was a partner in a modestly successful movie production company back in the 1970s and 1980s, and he also was part owner of an independent art house movie theater in a college town. He told me that published revenue and cost figures in the movie industry were completely meaningless from a financial perspective. He finally sold his interest in both the production company and the theater because of his frustration over the opaque accounting.