The more time spent on secular studies the less time there is available for Limud Torah, which is far more important. It is impossible to give a “public school equivalent education” PLUS a full Torah/Jewish education. There aren’t enough waking hours in a day for a child to have two such full curriculums.
The problem is that secular education has gone way beyond teaching the basics. It’s been perverted into a means of indoctrinating political and social viewpoints. Teaching the essentials of communication and quantitative skills, with a bit of history and geography, wouldn’t take that much time.