$440m sounds like a lot but it's not necessarily. That's over the life of the business, as I read it.
Let's say he's pulling $60m a year now. Or, heck, $150m. That's $10m per gallery per year. Gross. These prints are not free to print and frame and ship, the rents he pays are astronomical, and many of the staff need to be paid at least a little. Sales will be largely commissioned. But it's not ALL sales people.
We could be looking at $10m per gallery per year. We could be looking at $3m or so. Reality likely lies between them. Expenses could be anywhere from $1m a year to several million.
So is he making money at all? Who knows. The cash flow is outstanding, though!