I dont think so. I had a go on a 17.2 and felt so so high up but when I got back on my 16.2, I felt like my feet were going to touch the floor. He felt tiny and Im 5' 7 too. Friend said I looked good on the bigger horse.
i'm 5'4" and apparently looked tiny on a 17.2 and minute on an 18hh but another 17hhish that i used to ride i looked ok on cos he just had long legs. i think it depends on the build of the horse and rider. tbh most people i've seen on hunter types look small and at 5'7 i think you'll look normal
im 5'6 and ride a 17hh horse. Think lot has to do with build and nature of the horse. My one is quite compact and lot easier to control that a 15.3hh irish draught mare of my friends that i occasionaly ride. I tried a few horses out around 16hh and i felt big on them. The only thing with big horses is they need to def have manners when u are handling them on the ground - they are too big to barge around need to respect u!!!