It cost that much because it's an all in one, not because it's nice. All in ones are crippled by laptop hardware in what is largely used as a "desktop" solution. Without knowing the exact model of what AIO you have, I can't tell you exactly why you're getting terrible FPS in your games; but I can tell you it is likely due either to your lack of a discrete GPU or lack of a quality discrete GPU. The ones that I can see from a quick scan that are over $1000 have mostly Geforce 930A GPUs in them... They're older, they're gimped by DDR3 memory, and they do not have strong cores. The others around the price that you stated have a GTX 950m or just Intel HD graphics.
Run DXDiag--Win+r then type in dxdiag and press enter. There will be a tab once it finishes called Display, and there will be a subset Device. If you could tell us the Name: of that device, that would narrow it down likely.