I press my seams open and when I stitch in the ditch, I am stitching on the stitching. The needle and stitch sizes are different and I haven't had issues with thread breaking. For most of my quilting career I've used Dual Duty thread for piecing and quilting both. I call the to the side or 1/4" off "echo quilting".
For the last couple of years I've been doing a test with So Fine as my bobbin thread -- but I haven't gotten any of these tops quilted down yet so no experience with modern threads. I am, however, about to do some quilting down -- but mostly as free motion all over designs and not in the ditch.
There are still times when I want minimal quilting and a simple grid in the ditch is my deliberate choice, even with other options available. For "functional" quilting and now that I have a machine that does it, I'm finding the serpentine stitch to be my preferred option in similar circumstances. I like how that S shape stiching gets the seams on both sides of the line, I feel it holds up to machine washing well too.
As I evaluate the quilts I made in the 70s, my issue was that I did not quilt together closely enough and the fabric in the unquilted areas wore/rotted away faster than the fabric or seams in the quilted areas. The seams have lasted together strong and proud!