Your bandwidth allowance is probably a lot higher than most. And yes certain routers will prioritize traffic to minimize “bufferbloat”.
Variance happens for many reasons. The Ping, Latency, Jitter thread walks through it. Ping, Latency, Jitter …
True, some people use software and or services to manage transmission timings of packets. For example they use the software to slow down transmission of movement/action updates which emulates high ping. But they keep inbound and hit claim transmission normal. Typically with this type of software you don’t see latency variance though.