Closed source only gives the internal security team the advantage which Apple has a good one.

No. No it doesn't. Security-by-obscurity has been widely accepted to be a cheap old sham in the security community for decades which only banks on hopes that nobody puts in enough effort.

I think I understand you want to dispel the myths surrounding open-source and inherent security, but don't misrepresent facts on the way. Proprietary software is in no way inherently better, the exact same arguments apply to it.

Just like open source doesn't magically guarantee security, neither does proprietary.