They're a mixed bag because they're benchmarking libraries more than they're benchmarking runtimes. Often the JRuby-specific versions of libraries (e.g. activerecord-jdbc) do not get the same performance attention as the ones for MRI, and as a result they perform worse.
I know this is small consolation, but everything in the JRuby ecosystem is continuing to improve every day. When there's specific reproducible cases where we're slower, we take them very seriously.
I haven't seen any newish real world benchmarks to that effect though.
These web benchmarks give some conflicting results between MRI and JRuby : https://www.techempower.com/benchmarks/#section=data-r10&hw=... .