Well, I find for frameless packs and even Very light "framed" packs, it depends nearly entirely on HOW you pack your pack for how it feels on your back. IE how you use your pad, sleeping system, food etc to pack your pack. Weight distribution. Volume distribution. This will determine how the pack moves etc.
The first few times I went frameless, it felt awful, till I stopped a couple miles down the trail, threw everything out and started over till I got it right.