The main disadvantage of the audio visual approach is that it does not encourage the students to continue to learn as the grade achieved serves as an end to the process. Many students taught by the audio visual approach despite getting high grades could not communicate or speak well. They may be able to write well but ‘good’ speech is not inherently something that they can do years afterward.
The main drawback of the communicative language teaching approach is that it is commonly short- usually months only. It does not dwell on drilling; instead it covers the various ways of communication with contextualization, translation and speaking skills. During the study period, various role play and group projects may be used but if the student does not and cannot speak up then the approach may be considered to be unfruitful.
Therefore the best approach may be a combination of both approaches. It can be tailored for younger students by being closer to the audio visual approach and the approach for older students being closer to the communicative approach.
Of course the approach chosen depends on the attitudes and biases of the teacher. He or she may favour one approach over another and so may implement an approach closer to their ideal; flawed though it may be.
The way to reduce this problem is to educate all potential teachers the advantages and disadvantages of all approaches to language teaching and learning. Any approach is just a style and as styles go some get fashionable for a period and then another approach may get fashionable while the earlier approach loses its favour and number of adherents.