There's no doubt about the brilliance, the sincerity and the righteousness of the early Muslims. They did excel on an individual level and conquered great swaths of territory, but clearly failed to build institutions. The institution of Khilafah could not survive even for 50 years. In the absence of institutions, people become imitators, 'personality worshipers'.
Also, Islamic historians never fail to mention the 'welfare state' of Omar, but wasn't this 'welfare' limited only to Madinah? The maal e ghaneemat that came from the conquered territories, was it distributed equally in the whole empire, or just among the citizens of Madinah?