I am that lady that the LongArm quilter refered to... I have made many many quilts in my 40+ years of sewing and quilting.
I press my seams open because I like a flat block. In all my years I have not had the seam fail because of it. I tried the press to the dark ..( after an severe encounter with a quilt police) but all to often it resulted in more seams with 4 layers of fabric , where it was impossible to press to the dark and not have this intersection of quadruple layers.... not the flat block I intended.... so I press open..... all the time! When I do quilt my own and use stitch in the ditch ... I also stitch right on the seam , having it open makes it easier to land that stitch right on the seam line.
As for stress on a seam .. I have done my own little lab experiment and sewed a seam on scrap fabric with the same thread for both and pressed both ways ... and tugged directly on the seam ..... guess what ... no difference.
Pressing to the dark , was favored by handquilters, so when they quilted on the light side there were not as many layers to stitch through. Many of the older hand quilted quilts had alot of echo quilting so it was much easier to stitch around the lighter background fabric to make the darker shape have more definition.
As for bearding.. that was an issue prior to bonded fibers and the use of scrim in battings. Bearding can happen through the fabric , not only just the seam.
Each quilter finds what works for them and appeals to their desired outcome. Find what works for you and makes you satisfied and proud you are a quilter.