From the preface to Isaac Watts' Hymns and Spiritual Songs

At their importunate and repeated Requests I have for some Years past devoted many Hours of leisure to this Service. Far be it from my Thoughts to lay aside the Psalms of David in public Worship; few can pretend so great a Value for them as my self: It is the most artful, most devotional and Divine Collection of Poesy; and nothing can be supposed more proper to raise a pious Soul to Heaven than some parts of that Book; never was a piece of Experimental Divinity so nobly written, and so justly reverenced and admired: But it must be acknowledged still, that there are a thousand Lines in it which were not made for a Saint in our Day, to assume as his own; There are also many deficiencies of Light and Glory which our Lord Jesus and his Apostles have supplied in the Writings of the New Testament; and with this Advantage I have composed these spiritual Songs which are now presented to the World.  (Emphasis mine)

Compare to this:

All scripture is given by inspiration of God and is profitable for doctine, for reproof, for correction, for instruction in righteousness; that the man of God man be perfect, thoroughly equipped for every good work. (2 Tim 3:16,17)

Is Ike saying that there are parts of scripture that are insufficient?  I  don't believe that we are limited to singing the Psalms in worship, since there are many instances of non-psalmodic singing in scripture that is accepted by God.  But, we shouldn't presume to think we can improve upon what God has provided, should we?