I live on about $2300/month in a MCOL area with a child and a large dog. Here's how my monthly budget looks.
920/mortgage/insurance/taxes
40/internet
10/netflix
$250/car/health/life insurance (this is only for one person, as my child is on different insurance)
$350/utilities (this is high, but has a lot to do with the city and state I'm in)
$200/groceries
$100/pet food (I told you she was large)
$200/spending (includes gas, restaurants)
$200/month set aside toward vacations and holidays (also used as my emergency slush fund as it's easy to cut down on vacation spending if I need a new water heater)
$50/month set aside for misc, non monthly, expenses (car registration, back to school shopping, etc)
From what you've shared, it sounds like your son pays less in mortgage by $120/month, and doesn't have a dog who costs $100/month. This would bring my monthly budget down to $2100/month (including a $200/month buffer that I have allocated purely to planned luxury spending). He may not need to spend so much in utilities. And while he probably spends less in insurance since he is employed, he has prescription costs as well so that may even out or may be a difference one way or another. In addition, if I wasn't making more than this, the $200/month I am allocating toward holidays and travel would be going to savings instead.
In my opinion $2000/month is a pretty ideal budget for one person. It's tight if that's *ALL* the person makes, as opposed to being what the person chooses to spend, while amassing savings. As a parent I'd be a little nervous watching my child leave the nest on a tight budget and a low income, but as a logical person with frugal habits, I'd be damn proud. I think you should be too. Your son just bought his first house and has a plan to become independent despite struggling with chronic diseases.