You just missed the cheap AC68U's alternative, the Huawei WS880 

Asus Merlin firmware is nicer than other firmware (other brands), many features are being offered as well including games boost mode, adaptive QoS which you can use to prioritize the traffic to your games, I feel like banging the wall every time I see the green and simple interface of TP-LINK router, too get used Asus already 

C7 is able to handle 8 devices at the same time but might have problem when there is a lot of traffics to handle because the latest V2 only comes with a single core CPU. AC68U carries a dual core CPU (800MHz) and is having the similar chipset with the one in WS880 which only costs RM 199 few weeks ago. Another option would be C9, around RM 700 and is even faster than AC68U (1GHz dual core AC 1900).

Changing the router will not guarantee to have significant improvement to gaming as there are many factors that can contribute to bad latency, WiFi band/interference/bandwidth hogger/ISP etc. If you have tested the latency when using LAN cable and found no issue then high chance it can be solved by getting a high end router.