No, the issue w/ using the Util classes is that it removes the direct dependency on the service itself so your code can start even if the actual service you're using isn't ready.

So, for example, take DLFileEntryLocalService (the service interface) and DLFileEntryLocalServiceUtil (the legacy static class). If you use the util class, you have no direct dependency on the service itself so OSGi will start your bundle whether or not the service is actually available.

When you use @Reference and the service interface to inject into your module, OSGi is aware of this and will only start your module once all dependent services are started. This will block your module until all dependencies are ready.

Granted you might think that a core service doesn't have these problems, but they do still exist especially during startup (your module might start before the Liferay service has finished).

So no, you never want to use the util classes ever again if you're doing OSGi development. The only reason the util classes are there is to support legacy code that used all of those static classes from previous Liferay versions.

But any new development should only go through the service references and never the util classes.