There is no endpoint in the API that will give you user_info objects across the network.

The two end-points you've found is the way to go: 

- fetch all associated network_users for a user
- call for each network_user per site /users/{userid} to collect the user_info objects for the other sites the user has a profile for.
- combine / merge the data you've fetched for your goal.


See also: https://stackapps.com/questions/4493/getting-global-information-stack-exchange-about-a-list-of-users?rq=1