QOS is off at the moment. I use Netlimiter on my PC to cap its usage. It's Overwatch I noticed as that's what I mostly play.

@bobsa 

Netlimiter is a software-base traffic shapping program.  However this does not change how the router handled incomming and outgoing traffic. What is likely issue is resource usage.  If you are using 75% of your bandwidth for downloading that will in all likelyhood cause network perfomance issues for other devices while the download is in place,  regardless of how much bandwidth you have left for other devices.  If you are going to use such a program i would suggest setting the speed limit to 200 Mbps or half of your network speeds.  Remember in most cases ISP speeds are "Up to"  and most only gaurantee 80% of your package rate.  

@Carl I've since used QOS instead and given my PS4 %60 traffic priority and temporarily disabled netlimiter. Yet, I still experience the lag in game when downloading on the PC. So maybe it is the download using up all the hardware power, even though it is not using all the traffic. I thought this device was quite powerful when I bought it, but maybe not to today's standards.

Are you aware of anything uneeded I can turn off to try to free up router resources? Or a way to monitor which device is using up resources?

@bobsa 

Under system tools there is a traffic statisitics setting you could enable and monitor it could tell you by IP address where the network resources are being used the most.  Also under the USB settings there is an Offline Dowload feature that can store downloads and install them at a later time.  Thus allowing you to pull downloads and less used times.  You can look at the User guide for more on this feature. 

https://static.tp-link.com/res/down/doc/AD7200(US)_V1_UG.pdf

Those items is where i would start though.