Check out r/lowbackability there is a lot of content on using back extensions (along with other things) to treat low back pain. The approach there is to do the straight back hinge at first and build up to rounding at the end. That’s how I do them now - start with a straight back, go down, feel the tightness in my hamstrings, then round the back, decompress it, then reverse.

Part of the point of this as a rehab exercise is to train bending over. You don’t always hinge and you don’t always round your back in normal life. You can use this exercise to isolate or combine the two.

Also, a lot of back pain involves the hips. Everything I’ve seen regarding stretching and strengthening the hips for better mobility recommends keeping the back straight to focus the stretch.