I don't agree with Symfony being inherently "very heavy". As set of framework components, you can any part you find useful, and wire to together yourself, if necessary. e.g.
I would have to question how relevant a piece of core plumbing is to a regular user of the framework, as a regular user of the framework would likely never come across this class.
Also if you're working in the domain as a Symfony core developer, the idea of a ContainerConfigurator is not so insane, if you're developing a dependency injection container.
https://symfony.com/doc/current/configuration/micro_kernel_t...
Many other PHP projects, such as Laravel and Drupal pick-and-choose Symfony framework components in this way.