A few months ago I read an article about faith and reason; a couple points follow.
The scholarly arguments that the Koran had nothing to do with the Archangel Gabriel are vast, and easily available. The scholarly arguments contend that the Koran consists of a much later hodge-podge of poorly edited and contradictory material, much of it cribbed from easily-identified Jewish and Christian sources.
If the Koran is a 9th-century redaction rather than a 7th-century revelation, of course, Islam has a serious problem.
It would make Islam a variant on the Arian heresy.