Thank you for your question.
You're quite right. The level for citizenship is uniform. It's CLB 4, which is basic language proficiency in English or French. However, as you mentioned, many skilled workers come in with a significantly higher level. I referred earlier to that list of acceptable evidence that applicants can provide for citizenship purposes, and that includes a test that a skilled worker may have already completed as part of their process of immigration to Canada. They could reuse those results for the purposes of applying for citizenship because their level was already significantly higher coming in.