Role
System AdminSubsystem AdminTenant Admin
How role is given

From the user's profile page/edit modeFrom the user's profile page/edit mode From the Tenant Setting page
Who can assign the role
System Admins
System Admins, Current Tenant Admins
System Admins, Current Tenant Admins
ScopeManage all subsystems and tenantsManage only the subsystem he/she is assigned to
Manage only the tenant he/she is assigned to
Create/Manage Campaigns
In all subsystems and tenants

Only campaigns of the subsystems he/she is assigned to
Only campaigns of the tenant he/she is assigned to
Create/Mange News
In all tenantsNAOnly news of the subsystem he/she is assigned to
Add/Edit Users
In all tenantsNA
Only users of the subsystem he/she is assigned to

Edit Subsystem setting (workflow, role, submission form, reports homepage, etc)In all subsystemsOnly the subsystem he/she is assigned to
NA
Edit Tenant setting (tenant welcome strip, tenant categories, etc)
In all tenantsNA
Manage only the tenant he/she is assigned to
Edit System setting (GDPR, Profile fields, Features Global Setting etc.)YesNANA

To know more about other differences, read this document