Money might not buy you happiness, but it does buy you choice, in a way that poor, or even 'average' people will never have.
You can choose to quit work and travel round the world, or do voluntary work, or just sit around the garden drinking sangria.
You can choose to send your children to the best schools
You can choose to eat out every night and never have to worry how to pay for food.
You can choose to have the best of everything, and never have to worry about how to pay for the basic bills.
Yes, your job might be stressful, but you can walk away from it if you choose, and live a more 'normal', less stressful life. It's your choice not to do that currently. Most people don't have these choices.
If you are facing health issues at any point, you can afford the best private healthcare. It might not help, but it makes the whole process less stressful.
Money doesn't guarantee happiness, but it's much easier to cope with life when you are rich, so happiness is more likely, or at the very least, stress and problems are easier to cope with.