Well the options aren’t just capitalism and socialism. There’s also worse capitalism. So a normal capitalist system that protects itself does not just prevent socialism, it also prevents worse capitalism.
An example of a system that turned to worse capitalism is Nazi Germany. That’s why today, Germany prevents system change, so as to not again change from normal capitalism to worse capitalism.
A class of 200 students performing much worse than the last class is very unlikely. 200 Students is enough to make even small differences statistically significant.
A single test being much harder than the last test is much more likely, since it isn’t an averahe of 200, it’s a single datapoint.
That’s why if this semester’s class performed much worse than last semester’s, you can assume it’s because of the test, not the students.