It’s more complex than that I think. When you get really good at it, more clients come to you, and the quality of the client also increases. So you have more leads, fewer dud clients, and the privilege of picking and choosing which of those leads you want to pursue and which to pass on based on your strength and interests.
Yes, those just starting out will not have built up business enough to have any of that. So when you start out you do have to “pay your dues” to some extent and take anything that comes to learn and grow.
But that’s not a great long-term freelance business strategy. So it’s important to know that places like Upwork are stepping stones to better things. Leave them as soon as you’ve outgrown them and have the ability to attract clients on your own.