Nothing wrong with what you have now. With a decent OC, that Ryzen gets real close to an i7-8700k in performance, which is usually well above the monitors refresh, so upgrading the cpu isn't really going to show any benefits unless your current fps while gaming is under refresh.
For example, I get 300fps in cs:go. My monitors are 60Hz. So it'd be the same performance at 200fps or 400fps.
With a $300 budget, going Intel would hurt, you'd need a mobo and cpu, the ddr4 is transferable, sticking with Amd, you could go for a 2700x (after a bios update), but you'd still be only a few fps higher due to better IPC on the few cores games actually use since you'd still be right around 4GHz anyways after OC.