Even if smth impacts performance, it impacts performance for all of us. So old x265 codec etc doesn't affect relative performance. We use superpi benchmark that uses ancient algorithm for 3 decades, able to somehow compare raw single thread x86 performance between cpus without SSE and latest designs.
Benchmarks here are valued for their consistency, ability to compare through database that was collected for ages.
Why would we change x265 to better algorithm? To put zero value on older 100000 scores that were done with slower codec?