Its really not a serious question. Without having minimal language, math and science skills, young men and women coming out of yeshivos and BY’s will be functionally illiterate, unable to perform basic functions of paying bills, booking travel arrangements, communicating with medical and service providers, etc. You cannot keep the next generation in a cave forever.
That’s your theory coming from your very closeminded view that education has to take the form you are accustomed to.
But it’s demonstrably untrue, as chassidim who receive a very poor secular education (which I’m not agreeing with, but it’s none of mine or anybody else’s business) make more money than the average, and are able to communicate just fine, even if their grammar isn’t perfect.