Reading Arabic letters means paying attention to detail and where dots are located, especially when you first learn the language. Not an issue after that.
I fail to see how that is "hard for the brain", when you know that the Arabic alphabet is limited to 28 letters.
The OP should have looked at learning languages that have thousands of ideograms (Japanese Kanji, Chinese, etc...)
>Even in online writing, people mix standard Arabic with their own dialect or major dialects.
When that happens, it just shows a poor command of the Arabic language.
>It's like learning Latin, Italian, Spanish and French at the same time.
Let us not make it harder than it actually is.
I would say it is like learning English for the writing part, but also knowing a few words here and there like "Bonjour", "Hola" and "Grazie" for when you talk to people in various regions (in addition to the English language that they would all understand...)
>If you understand Classical Arabic, Modern Standard Arabic, Egyptian, Syrian, and Iraqi dialects, then you can communicate effectively with 90% of Arabs.
If you learn Classical Arabic (this is what you would learn at school, not any of the dialects), and you learn a few important words from the following oral dialects:
Egyptian, Syrian, Moroccan/Algerian