Throughput matters very little in online games, because games don't send/receive a large amount of network data. Latency, however, is very important because the timeliness of data in online games is the difference between winning and loosing.

Throughput is defined as the amount of data per second that can flow between two endpoints, and is almost always limited by the ISP.

Latency is defined as the round-trip-time between two endpoints (regardless of the amount of throughput). 

Usually there is a tradeoff between Throughput and Latency. Killer has been designed for low-latency because it is latency (and not throughput) that affects online gameplay. Throughput does not matter in online gaming or daily web surfing because it is limited by the ISP.