Azure Lighthouse focuses on Azure tenants (not M365.) Microsoft does offer M365 Lighthouse for some visibility and limited remediations across M365 tenants. They also offer tenant-specific methods via Defender, the app admin portals, etc. The difference with Security Manager is that it starts with a cross-tenant perspective. Actions can be performed across all or a targeted set of tenants. Also, it's focused on automating these tasks, not simply giving you an alternate portal to perform them one-by-one. Add to that the deep reporting, scheduling, and customization capabilities and you'll see that Security Manager has been built specifically with the MSP's needs in mind.