> ZGC will have a <1ms worst-case latency

In our benchmarks we never saw a GC pause of more than 2 ms on either ZGC or Shenandoah, but the end-to-end latency, the one the user cares about, is impacted by much more than a single GC pause. Sometimes there would be several pauses in a rapid sequence, or just the background GC thread would do too much work at once.

Even after dedicating a core or two to the GC, you still face the issues of cache pollution and RAM throughput stealing that heap walking incurs.