Given that the purpose of a measure is to make predictions: IQ can be used to improve predictions of academic outcomes, whereas the multiple intelligences models are worse at this.

Whether or not there are multiple intelligences or not is an implementation detail unless knowledge of this has measurably lead to some better prediction.

There's no actual IQ test. Any data you've ever seen using "IQ" to predict academic outcomes is actually just using prior academic scores bent into the shape of a symmetric normal distribution.