The Arabs were actually fairly nice, as period conquerors go. They didn't go out of their way to massacre people or demolish the very foundations of local culture - compare what happened to Mesopotamia during the Arab takeover, and what the Mongols did to it - and actually weren't even too interested in converting most infidels (although the reasons for that were pretty base). Where they went they usually melded into the local culture and populace, although they usually left a mark besides religion. Persian culture, for example, did not particularly suffer from the change of overlords and even the old ruling class largely kept its position - and later on the region would become a shining jewel of learning and high culture.

Well, it never really recovered from the Mongols, who on the side irrecoverably demolished the sophisticated irrigation system that'd fed Mesopotamia since men started building cities - all the engineers got killed, y'see.

A pretty fundamental difference is that in many places the Muslim conquerors were hailed as liberators by the locals (Palestine and Egypt for certain; both the Jews and the Egyptian Christians had some serious grievances with Byzantium). The Mongols, well, weren't.

It is true that for the brief period the Great Khanate held together the Silk Road saw some serious traffic; many historians postulate control over its riches was what the Mongols mainly were after to begin with, and the infrastructure of the realm was on a serius upswing. Well, that lasted until the Khanate fragmented and the pieces started squabbling, which severely reduced trade along the Road for some fairly obvious reasons.

And that brief stability was only achieved after incredible bloodshed and irrepairable damage to both the economy, the culture and the very demographics of vast regions...

No, the Arab blitzkrieg doesn't compare to the Mongols at all. The Arabs at least were only partially nomadic, and could appreciate the ancient cultures they met. The sons of the high steppes didn't much care, and all too often just torched the whole thing and sold the surviving inhabitants to slavery.