I wonder how much of that is truly GC improvements vs. increased hardware speed dropping pause times.
With traditional low latency GC designs (e.g. Shenandoah/G1), faster hardware provides almost no benefit because the GC pause is based around the time for core to core communication which hasn't decreased much (since we keep adding extra cores so the fight has to be to keep it from getting slower)
The benchmarks don't necessarily use all of the cores though, and memory bandwidth has increased considerably since those original benchmarks, so you should expect pause times to decrease from that alone.