Dia memiliki banyak kelemahan, tapi menurutku ia tetaplah seorang sarjana yang hebat.

English Translation

He has some grave defects, but I think he is a great scholar all the same.

“Great” as an adjective doesn’t mean “many” (banyak) but “serious” (serius). “Dia memiliki beberapa kelamahan yang serius” would be better.