Those big numbers are why your back hurt. Press allows you to up the weight with less injury/pain concern so long as you don’t overdo it (and keep good form which is often what kills your lower back). Press compliments the squat and isn’t a replacement. Instead of the squat being my core quad exercise I can divide it with the squat/press therefor helping my knees.I find those machines you bought are a far bigger killer on my lower back than the squats. That’s why I stay the eff away from them. Got high numbers but lower back suffered for weeks afterwards.
With the squat Im hitting much lower weights, but enjoy it and feel it better.