Is hunting animals, crafting and attacking/defending from enemies intellectually equivalent to learning quantum physics?
Addressing some assumptions/presumptions apparently present in the question (this might be too long for a comment):

First, natural selection has not stopped. The sexual selection might be more active than ever, so there is ongoing "pro-fertility" selection and some segregation "pro-smarts". Not every member of contemporary potplation is capable, even with unlimited attempts at education, of doing something useful with quantum physics.

Second, surviving in the wild and fighting enemies are competitive enterprises. Which means that the task is of potentially unlimited difficulty: the better you are at survival, the more you procreate, the more pressure you put on limited resources of the environment, to harsher climates you spread. With enemies, especially those evolving along with yourself, this unlimited competitiveness is even more obvious.

So, the question could possibly be framed differently: how hard our ancestors, living in nature, made the intellectual part of the task of competing with each other? Apparently, about that hard.