You answered your own question really, but religious scholars and academics who speak Arabic as a second language. When I lived in the UK I met many from the Indian Subcontinent (Indians, Pakistanis, Bangladeshis) and Turks who only speak MSA, I also worked with Eritreans and Ethiopians who only spoke MSA. Children in the Arab world who do all their studies and watch cartoons in MSA can understand deeper topics in MSA as opposed to everyday topics in their dialect. As for Arabs in general, MSA is a prestige lingua franca in the Arabic academic world, religious scholarship, literary fields, politics and journalism so there are many Arabs who speak MSA better than their dialect but I wouldn't say they are extremely bad at their dialect. As an example my cousin works for Al-Jazeera and pretty much any topic non-related to food he would go full MSA and I'd have to follow suit. He quotes Nietzsche and Schopenhauer in Arabic though so he might be a special case.