Seems like Rampage, Blockers, and Ready Player One should lose more sites than BP next weekend. Considering Rampage only made 5M on its second Friday despite being in 4115 theater sites in its second weekend of release. I don't see it regrouping to surprise like Jumanji did given IW is scheduled to suck up all the air for the next several weeks. So lack of demand should cause it to lose theater counts. Blockers averaged only $670 per site yesterday and Ready Player One only $599 from 3134 and 3208 total sites, respectively. By comparisons, BP averaged $636 per site from just 1930 total sites on Friday. So, despite being in roughly 40% less theaters than both Blockers and RPO, BP is performing nearly as well or better on average.
If Black Panther were still in 3-4K theaters this weekend it might have pulled in 8+M to outperform Blockers, RPO, and Truth of Dare. I don't know how the agreements between movie distributors and movie theaters work, but some bean counter has got to be making a strong case for not slashing BP's theater count next weekend and the following couple weeks, but keeping it constant or maybe even increasing it a couple hundred theaters as IW's release approaches to at least test out the coat tails it might have on BP.
Some of your points are based on the assumption that every theater contributes (roughly) the same amount to the overall gross, but thats definitely not the case. The relation between theater count and theater average is not linear at all. A smaller theater count means the average remaining theater is bigger, which leads to bigger theater averages. For example, a theater in the middle of a big city will be getting several times more visitors than one in a small town. And since they're in a better location, they attract enough visitors to justify having more auditoriums than a theater in a small town, which means they can accommodate more movies at the same time.
The theaters that drop a movie first are the ones that dont have enough screens to accommodate a lot of movies at the same time, and those are the smaller theaters which attract smaller amounts of visitors in the first place. Because of this, you will often see a movie's PTA increase when it loses a lot of theaters. But obviously the PTA in the theaters still playing the movie will still have dropped like it does on any other week. Comparing 2 PTA's when the theater count is not similar is comparing apples and oranges. Lets say you have 2 movies: movie A has 4,000 theaters and a $600 PTA, and movie B has 2,000 theaters and an $700 PTA. If a theater is playing both movie A and movie B, which one are they more likely to drop? The answer is movie B, no contest. Even though movie As PTA of $600 is lower than movie Bs PTA of $700, movie As PTA in its top 2,000 most profitable theaters will be much higher than $700, and the vast majority of movie As top 2,000 theaters will be the same ones that are still playing movie B.
So if you were to multiply BP's theater count by 2 now, its gross would not even be close to 2x bigger, because the theaters it has lost are exactly the ones where it wasnt making that much to begin with. Black Panther would not have made $8M+ this weekend, even if it was still in 4,000+ theaters. Increasing the theater count that drastically would have a much bigger effect on the PTA that it would on the overall gross.
And maybe Rampage, Blockers and RPO do lose more sites than BP next weekend, but the vast majority of those sites will be the ones BP has already lost, not the ones where they are still competing for screens. In the vast majority of theaters where they are still competing with BP for screens, Rampage, RPO and Blockers will be making more money than BP, and therefore those theaters are more likely to drop BP than they are to drop any of those 3. Thats why those 3 will still have a bigger theater count than BP next weekend. The vast majority of the theaters that still have BP are the ones that have enough room to accommodate both it and those other movies at the same time.
And on top of all this, losing screens and losing theaters are also two different things. To make room for IW, many theaters will just lower the amount of showtimes for other movies, instead of dropping those other movies completely. Thats why you often see that movies have better holds on a blockbusters 2nd weekend. In the OW, a huge blockbuster (like IW) will need a huge amount of screens to meet the demand, and other showtimes will need to be cancelled to make sure that blockbuster has enough screens to meet that extreme demand. A week later, when the demand for that huge blockbuster is not as extreme anymore, that leaves a lot more breathing room for the other movies, making it easier for those to maintain their showtime count, and have better holds as a result.