Prebuilts often cut corners all over the place. Especially Walmart. Typically in the power supply, wiring, and other small things that no one looks at on a spec sheet. And the prices usually aren't much lower. Plus building a PC is fun, educational and will help you troubleshoot inevitable issues and failures in the future.
If you're feeling overwhelmed, PCPartPicker has a bunch of good builds at very price points and resolutions.
Arc Raiders is not a terribly demanding game.