Currently, there is 2 pages to track users in a team:
Users on plan shows any user that is counted towards the plan. This does not include users that have been added into a group but have no permission towards any team private repo.
Groups page. The groups page shows a list of groups. This does not include users that have been granted access to the repository directly.
When a team member leaves the company, the administrator will need to check 2 pages to remove the team member. It's also tedious to check the groups as there is no unified view of all group members.
To ease the process, Bitbucket should have a page showing a list of group members in all groups so users can easily search and remove users