Currently, the plugins that are only transitive dependencies in essentials.yaml and ingest.json can be chosen on older versions.
This leads, for instance, to generating warning or error logs that have actually been fixed already, sometimes long ago.
This is very easy to fix, we just have to declare all transitive dependencies directly under the spec.plugins node in essentials.yaml, but I'm a bit reluctant to do that: we would lose a bit the main plugins we do depend on and want installed, and the ones we only put there to force a specific version (and that we do not really care about if it had to be removed, say).
Evergreen installed plugins should (strive to be) always be latest.
So that we do not see error logs or behaviors in production that are already fixed in the given plugin.