Stardew Valley sold over 30m copies on a solo dev's work. I think you'd be surprised
I'm building my own product right now and never have I wished I had more technical help. It's all the other junk like sales, marketing, distribution, that makes the business so hard. Marketing and sales, in isolation, I've had success with in prior jobs. I'm a fairly productive solo developer.
However, being able to context switch and do both dev and marketing? Now that's hard. I have beyond massive respect for anyone that's even attempted it, let alone been successful doing it.