While I agree with you in general, a surprising number of grammatical features that make many other languages difficult to learn are missing in Indonesian. Some examples:
No grammatical gender
No plural forms of nouns
No grammatical case
No verb conjugations
No verb tenses
In addition, written Indonesian uses the Latin alphabet and has a very consistent phonemic orthography.
Of course, it also has some more complicated features, like formal and informal pronouns. But it still seems fair to me to say that it is grammatically simpler than many (most?) other spoken languages.