Hey Maria!
Thanks for this one, it's a great call out. Right now, Collaborators are tied to individual projects, so there's no way to save a group of people and pull them into a new project without sending a fresh invite each time. If you're working with the same subs over and over, I can see how re-inviting them on every Project gets old.
We don't have a saved Collaborator list like you're describing just yet, but it's exactly the kind of thing our product team wants to see, so I've passed your request along to them.
Requests like this one genuinely help the team figure out what to build next, so thanks for taking the time to write it up. Keep 'em coming!