Bronco Wrestler, your math is only half right. If there were twice as many schools in 5A and 6A, they would not only have twice as many wrestlers, on average, with losing records, BUT they would also have twice as many wrestlers with winning records, on average.

The reason for more wrestlers with losing records making it to state in 5A and 6A is strictly due to the fewer number of varsity wrestlers total than in the other classes. With 8 teams at each regional, at least half of the wrestlers are going to make it to state, period.

Obviously, some of those kids are going to have a losing record (we can assume that half of them do on average across all weight classes each year). Some of those kids with losing records are going to place at regionals for a variety of reasons (they've improved enough during the course of the year to become better than the kids with winning records, or were always the better wrestler but saw tougher competition, or just plain wrestled better than the competition on that given day).
Statistically, the numbers say that is going to happen far more often in 5A and 6A.

If there were twice as many 5A and 6A schools, the number of wrestlers with losing records making it to state would almost assuredly be far less (due to more wrestlers with winning records to compete for the 4 state qualifying placings at the regionals for each weight class). In fact, we would probably see numbers similar to the other two classes, since the total number of varsity wrestlers per class would be similar if there were twice as many 5A and 6A schools.

So, it is all in the numbers. Statistically, it is easier for one with a losing record to make it to state in 5A and 6A, on average.

If one wants to use that as the only criteria to decide which class will have the toughest state tournament, the answer is in the numbers. But I think that would be a very poor criteria to use by itself to determine the "toughness" of each class' state tournament. There are lots of other factors that should also be considered to make such a determination (many of which have been discussed/debated/argued, etc. elsewhere on the forum).