I don't see a real problem. You have two successful kids and one kid that has been dealt a more difficult hand, but that is also going to make it.

He is spoiled because you pay his tuition and his books?

What exactly is he doing that is decadent?

He should get a job? Then why is he in college? You want him to leave college and get a full-time job on his AD? Working a job as a student costs you money because you'll graduate later.

Sounds like you are getting on each others nerves and you don't appreciate what you are doing for each other.

I was in a similar position and had parents that basically only had to offer me money. Not saying you are the same. But if my parents refused to offer me the money they had, didn't need, and I needed to not be a failure in life, they'd have exactly 0 to offer me.

Maybe he can cook his own meals and clean up his own stuff, sure. But why have him run separate laundry?

Maybe his allowance is too high and maybe you are spoiling him. But if you take it away 'because we have been bad parents that spoil our sun', he has less money and has parents that admit to being in the wrong. Doesn't fix anything.

Every child deserves parents that do almost everything for them. If the child is ungrateful or doesn't appreciate it, that's not nice, I understand that. But it doesn't mean the child needs to be punished and have his life be made more difficult.
If I was a parent, I would be more worried about a child never coming to meet me after they no longer depend on your support.

If he is not being too independent enough, talk about him living at his own place. It costs you more money, yes, not less. The whole thing about teaching a child to money manage, that's important, yes, and a subject on itself.
Don't be too afraid about having your child fail and learn from mistakes. Just don't withdraw support. Giving t your child the freedom to make mistakes and have to suffer through them and learn is different from not being a supportive parents.

If you just don't have the money he needs/demand, not that's a different issue. Anyway, who makes the money? The father? The mother? Both? I mean, it is always going to be unequal inside a family.