Let me preface this by saying this is just my experience personally,

As libyan, I can confirm that your statement is likely accurate… I can understand Tunisians 90%-95%, Algerians I would say 60%-70%, and Moroccans.. well it depends on the region on where they’re from tbh but it’s significantly more difficult than the rest of the Maghreb region.

As for ME dialects, I always found Iraqi (in some cases even harder than Moroccan) and Yemeni the hardest two dialects for me.

And as you indicated in your comment, it’s all to do with geographical proximity. I would also add the factor of exposure… because at the end of the day it’s Arabic tbh