Same views here. If you notice carefully, all the conquests and spread of Islam was done by the first four caliphs. After that, little land was gained anymore and people in those newly conquered lands did not convert to islam. The original islamic zeal was absent.
It leads me to think that up to caliph Harun ar rashid, Islam was in its original path. After that, it evolved to greed, lust and hypocrisy. No wonder muslims never won any decisive war in the last 500 years or so. Whereas Quran promises that God will give victory to believers if they really believe in him. Makes us wonder, are muslims really the "believers" as God meant for muslims to be? Well, all evidence points to that their motivation was rather by greed and lust rather than belief in God.