Isn't this already part of the @Symfony or @Symfony:risky rulesets ? This is a rule we have since years in the Symfony coding standards.

Nope https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/master/doc/ruleSets/Symfony.rst.
Do you think it should? I tend to think it's fine to enable this one only on the core codebase.

It mentioned in https://symfony.com/doc/current/contributing/code/standards.html

Add a use statement for every class that is not part of the global namespace;

But not applied in https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/master/doc/ruleSets/Symfony.rst?rgh-link-date=2022-10-26T12%3A10%3A34Z

I think we should fix the rule set instead of the core config

Works for me: PHP-CS-Fixer/PHP-CS-Fixer#6662