I ran an advertising agency with employees at one point and grew it to $50k/mo but hated it so stopped and went back to single founder SaaS stuff.
Before the recession hit, I also ran a SaaS product in the Real Estate sector that brought in over $70k/mo at its height. I had a few employees during that time too.
I personally enjoy being a single founder running niche products but it has its downsides. Also, once you reach a certain growth point, it becomes much more difficult to go it alone. At that point, you can either hire employees to help or decide maybe it is best to sell.