This seems to depend very heavily on the company culture. Which one do you think is the right way to think about the field, and which one do you prefer?
Very much a team sport -- this is one of the reasons we started Taro!
Jordan talks about this in his video about the difference between school and work as an engineer. You're no longer doing projects or problem sets in isolation. In industry, you need to work with a team to get things done. Onboarding, code review, running experiments -- these are all best done with multiple people.
Another way to see this is that one of the most important criteria for a startup is if you have a cofounder, and how strong your relationship to that cofounder is. YC talks about this in their FAQ: https://www.ycombinator.com/faq
100% a team sport, all the way through. Some examples include:
When you first onboard, your team is there to jumpstart you so you can start contributing.
When you open up a new PR, your team is there to make sure your code looks correct
When you come up with a design doc, your team is there to provide feedback
When you work on a roadmap, your team is there to discuss the tradeoffs in working on certain projects over other projects
If there's an upstream service that is causing your feature to fail, you are dependent on another team to fix any issues with their service