Escribo is more common than estoy escribiendo though, right?
Well, I don't know in American Spanish, but in Spain it is absolutely common and completely right. As far as I know it is as in English, I mean, "Escribo todos los días" vs. "Estoy escribiendo ahora mismo".
However, it is true that you could hear the simple present some times when the continuous form would be used, for example, someone calls you and asks "¿Qué haces?", but then you answer "Estoy viendo la tele." Anyway, the question could possibly be "¿Qué estás haciendo?" too.
I must say I've always been shocked by the parallelism between the "present" vs. the "present progressive" tenses in both English and Spanish.
Now if in traditional Spanish grammar, estar + gerundio is always analyzed as a verbal periphrasis and not as a "compound tense" (as it is in English), that's another matter.
The reason I compared them is because I had assumed all the present tenses in Arabic were the same...at least I had thought as much since Arabic works off the perfect/imperfect system.
Yes, you're right. But you can also use other options to express more concretely the tenses, such as particles or, as in this case, the active participle (I'm not sure if it's called like that in English, but I mean the form فاعل).
Yes, that's how it's usually called in English.
Actually, all this time I've been studying Arabic using English-language books only. Would you mind telling me how it's usually called in Spanish (if you happen to know)?
Something important to mention about this use of اسم الفاعل (the active particple), is that it has no sense of time. In أنا فاعله, it could stand equally for a "past progressive" ("I was doing it", although كنت أفعله kuntu ’afʕalu-hu would probably be more common here (and yes, Arabic has a few "compound tenses")), "present progressive" ("I'm doing it") or "future progressive" ("I will be doing it").