I don't think that is fair to say. There are lots of other languages that lack most/all of these features (e.g. Mandarin has no gender, limited number marking, no case marking, lack of inflections). Indonesian is not unique in that regard.

Indonesian verbs lack the tense, number and person agreement marking that is commonly found in European languages, but they have a lot of derivational morphology including complex voice and valency operations (Austronesian alignment[0], causatives, applicatives etc.)

Indonesian also has noun classifiers like Mandarin which have to be memorised like grammatical genders.

[0]:https://en.wikipedia.org/wiki/Austronesian_alignment