That was back in 2002, so there's certainly been a lot of scrutiny since then. In particular, I've never actually read about Java sorting benchmarks, but there are tremendously sophisticated benchmarking tools/benchmarking experts in the Java world, so I imagine that it got a lot of analysis there.
It's worth noting that Java doesnt exclusively use Timsort. Depeding on the data type and heuristics based mostly on the size of the input array, a simpler sort such as counting sort may be use.
You can also read Tim Peter's notes about the sort: https://bugs.python.org/file4451/timsort.txt
That was back in 2002, so there's certainly been a lot of scrutiny since then. In particular, I've never actually read about Java sorting benchmarks, but there are tremendously sophisticated benchmarking tools/benchmarking experts in the Java world, so I imagine that it got a lot of analysis there.