if you think the plant manager should be exonerated because he folowed the rules, you are siding with deontology, whereas if you think he should be punished because a death occurred under his supervision, you are siding with consequentialism
This is missing the point. Consequentialism is about making decisions, not about judging past decisions. Consequentialism says that if punishing the manager would (in expectation) have better consequences than not punishing them, then they should be punished, and otherwise they shouldn’t. Deontology says that if the rules say to punish the manager, they should be punished, and if the rules say not to punish the manager, they shouldn’t be punished.
This ignores the possibility of advances in the teaching of math (or physics, or any other discipline). If improved teaching methods lower the level of intelligence required to reach a given level of knowledge, then a field can advance considerably.
Not to mention that the human population has been growing, and average intelligence has been increasing.
Finally, there’s specialization. It doesn’t take much intelligence to know everything that was known about genetics when Darwin was alive, but probably nobody is smart enough to know everything that was known about it in 2000. But there have still been make advances since then thanks to people specialized in subfields like DNA sequencing.