Squats are awesome for the back and quite safe unless done very improperly. If you can’t squat the weight safely, it’s too much for your legs anyway. You have an imbalance, by definition, if the weight that is appropriate for your legs is enough to put your back at risk.

Legs are stronger than your back. So a good load for the legs will probably be too much for the back. Also there is only a limited amount of repeated compression that the vertebral discs can handle.

> Legs are stronger than your back. So a good load for the legs will probably be too much for the back.

Well, yes and no. In unnatural movements like the hip belt “squat” where you have no range of motion and have almost created an isolation movement, sure. In more natural movements like a lunge or squat, where the muscles must work together and you use reasonable range of motion, not necessarily true. It’s more commonly the legs that fail in a squat.

You do realize that the glutes and hamstrings are part of the legs, right? They execute the hip hinge that makes bending at the hips possible. When you take the back out of a squat, you largely remove these as well.

> Also there is only a limited amount of repeated compression that the vertebral discs can handle.

This is a definite “citation needed” sort of claim. The spine produces synovial fluid and heals like the rest of the joints.

Obviously there are limits to how much it can heal, but that applies to every joint and consistently studies indicate better joint health among strength training individuals. A few dozen squats a week is definitely not the maximum the spine can handle.

I’m not sure what problem you’re trying to solve.

Back squats and front squats are good because they involve the posterior chain.

Often all of that has to work together. A squat with a small load will show you where you are deficient and will help you improve as you learn to squat properly.