This is easy:

Standard Jetbrains Runtime - slow as fuck, missing a whole host of performance improvements, security updates, and bug fixes since the fork occurred back in JDK8/9 Era.

OpenJDK - ugly as sin, gui becomes glitchy, lose out on customer support channels (first thing they tell you is to use the standard jetbrains runtime)

Newer versions of Jetbrains Runtime - have to reinstall manually every time you update your IDEs. You also lose out on customer support, as they are beta software.

This isn't really a hard problem to solve: find a way to upstream your improvements to the JVM, and then package the upstreamed version. All of these problems go away, and you're even relieved of the burden of maintain a long running fork.