The two sites have very different missions which are stated directly above the list of topics, so anyone who is taking the time to read the help topic you are proposing to change should see them.
What topics can I ask about here? (English Language Learners)
English Language Learners Stack Exchange is for people who are learning or teaching English as a foreign language.
What topics can I ask about here? (English Language and Usage)
The English Language and Usage Stack Exchange is for linguists, etymologists, and (serious) English language enthusiasts.
I don't think that excluding "advanced" questions from ELL will help someone distinguish the difference between the two sites when the sentence above the topic list makes it clear which site a person should post their question to.
If you want an answer from a linguist or etymologist because you're very interested in the English language (regardless of whether it is your native language), or your question is about etymology, you would ask on ELU. If you are learning or teaching English as a second language and would like a layman's answer1, you would ask on ELL.
The ELU help topic does direct some folks to ELL:
In addition, if you are new to learning English, please consider whether your question might be better suited for English Language Learners.
1 Some community members may in fact be professionals, but the type of answer they might give here would probably be more focused on the practical aspects of the usage than the answer they might offer on ELU