I disagree. There's no magic to being on call that means you understand something well enough. That's simply not automatic.
Following through with something from start to "finish" is far far more valuable than fixing one off bugs and then doing something else, and then something else.
If anything I think it can lead to a lot of poor assumptions based on very skewed experience.
Depends on the nature of your oncall. If your oncall is just following documented restart procedures when your app gets stuck, you won't learn much. If your oncall involves deep investigation into your system and how it interacts with other components (services, databases) etc you'll learn a lot.
per some sibling comments though, years of experience != veteran, to be clear. There's certainly people who have been working for 10+ years, sometimes even at the same company, and don't really understand what they're working on.
Following through with something from start to "finish" is far far more valuable than fixing one off bugs and then doing something else, and then something else.
If anything I think it can lead to a lot of poor assumptions based on very skewed experience.