Thanks for your comments folks. I agree in that if its not carrying much weight then the belt isn't needed as much, and that it can stop the pack moving around so much, but it still seems more of a waste than not in most cases
The only small pack with a hipbelt that fits me is a Golite Ion, which is a cracking little pack. The hipbelt is fairly narrow though and its a small pack so you can't put much in it but I do find the hipbelt useful nonetheless. Unfortunately mine is blue and now covering in reflective stickers as I use it when cycling. If I could source a black one I'd love it!
I haven't seen the OMM packs in person, if I saw one in a shop I'd try it on
Same for the sacks with more breathable back panels, like the berghaus freeflow series. Rarely do you find one that fits, I tried a variable back length one (Berghaus I think...) and it just about fitted but still wasn't great