> good tracing GCs have long ago surpassed manual memory management in throughput, and more recently their latency impact is more than acceptable for the vast majority of applications

There is a very subtle problem you seem to be missing: the GCs with high throughput are not the same as the ones with low latency. So while technically it is possible that tracing could beat manual management on one metric - throughput, latency or memory overhead, it doesn’t do on all of them together.