A Muʿtazilī interpretation restricts the forgiveness of lesser sins to cases of repentance. The response argues that if repentance is made the sole condition governing both categories, the verse's express distinction between shirk and what falls short of it loses much of its argumentative force.
The apparent structure states different rulings for the two categories. Adding an unstated restriction to one clause requires evidence; the need for repentance is not denied.
This is an interpretive disagreement over the scope of the statement, not an argument against repentance as a religious duty.