First, depression will definately make it impossible for a person to accomplish the most basic of tasks. If his therapist and your son both agree that his depression is under control then I'm concerned that any therapist would fail to recognize that your son's failure at school is clearly a sign that something else is going on. He/she should be working with your son to understand and articulate what is happening. Kids who "use excuses" are struggling with something and need help. His therapist should understand this and not be dismissive.
Second, you say you don't compare your sons but then go on to paint your older child in bad terms and your younger son in glowing terms. I promise you that your kids both know what you feel. They will try to live up to the roles of "good child" and "black sheep."
You say your son is lazy, but when he's not doing his school work he self initiated drawing activities. You may not value drawing as a skill but I assure you it has real value in today's graphics rich world. Your son's drawing is industrious. It's creative. It takes practice and dedication to develop this skill.
Perhaps you might step back and instead of looking at what he's having trouble doing, see what he is good at. Start making a list of all his positive characteristics. Start focusing on praising all his stregnths. When people feel seen and appreciated for who they are then they tend to do better in all areas of their life.
Instead of deciding between pushing him and "letting him fail" maybe talk with him about what he'd like to learn. You may find a video editing class, cartooning class, graphic novel development courses. You could help him find things online that will help him succeed in ways you might not have considered.
The more he feels seen, understood, and appreciated for who he is the more all boats will rise. Set aside the issue of the failing classes for now. Focus on helping your son see what a beautiful light he brings to the world.
Books that might help you: The Kazdin Method for Parenting the Defiant Child; and Duct Tape Parenting.
Good luck and hang in there!
