> First off, Oracle are doing versions at approximately twice the cadence

Is that actually a good thing?

But Oracle started playing a game, for better or worse, where they decided to couple the "language version" with a single specific runtime's release schedule. For example, in "Java 27" there are exactly 0 language changes and 1 minor feature addition to the TLS library.

Everything else is OpenJDK runtime internals which don't impact the language or how you use it. So if you don't use OpenJDK (such as if you use Oracle's other runtime, GraalVM), then Java 27 basically doesn't even exist at all. Skimming the past couple of C# releases, it doesn't look like Microsoft is playing that game, so the release cadence will of course be different.

You’re only counting JEPs, which are only for more involved features. There are lots of changes to the JDK apis that are used by other runtimes. See, for instance: https://javaalmanac.io/jdk/27/apidiff/26/.

Admittedly, the terminology here is almost designed to be maximally confusing, and I’ve never read a good post that laid out how everything relates.

There's not really a second C# runtime. Java has several, some based on the Openjdk, but a few that are completely new like OpenJ9 and Graal.

The closest C# has is mono.

This sort of thing is bound to happen with that situation. Heck, it happens with C++ whenever a new C++ version comes out. Some C++11 features took years to make their way into all the compilers.