The fact that many of the graduates of these religious schools go on to do well in university and in professional life afterward is proof enough that they are teaching academics at an appropriate level.
I was homeschooled using a Christian curriculum, have worked at a nuclear science facility for the last decade or so. So yes, they teach hard science just fine.
Both my kids are in the local public school, and it is my biggest regret as a parent that I allowed them to go there. I got a better education reading my own textbooks 2 hours a day than they get with "professional" instruction 7 hours a day. At 16 I could read at a college level, do algebra and trigonometry, had a good knowledge of world and US history and the functioning of government, the "education" my kids get at their school is an absolute joke.
Also, just because its a public school doesn't mean it isn't stuffed to overflowing with indoctrination. My daughter's French class has spent an entire month covering the French alphabet, kindergarten stuff, my son in high school has a 3 year math program that in that time period barely covers Algebra II. However, they are forced to listen to their liberal harridan teachers moan about capitalism, the oppression of the white man, the "structural racism" of the United States, how to properly use pronouns, acceptance of LGBTQIA+-LMNOP alphabet soup garbage, that religious institutions are filled with hateful racist people, that the people who burned down business districts because a criminal died in front of a camera are an oppressed minority who should be coddled rather than punished for civil disobedience.
Public education is a sewer of idiotic leftist indoctrination, and while they manage to brainwash a lot of kids into their degeneracy, those they don't turn from it HARD, and lose all faith in education as a system.