The Sagrada Familia is structurally far more sophisticated than the Akshardham. Gaudi's articulation of concrete columns and piers makes the Akshardham's engineering look like Legos. Take into account also the difference in scale, considering that the Sagrada Familia will be vaulting over hundreds of feet in the air without steel while it looks like the Akshardham is just corbelled blocks rising 50-100 ft; in fact, you could probably fit multiple Akshardhams vertically into the completed Sagrada Familia. Also to be considered is that many of Gaudi's plans for the Sagrada Familia were lost in a fire years ago and much of the new plans are conjectural. It is not at all an issue of ornamental intricacy, which is what you are comparing them with here, but rather of structural and scalar means.
Here is a diagram that shows what has been completed and what has yet to be built: