This is SharePoint on-premise, so Google Workspace isn’t a good comparison?

Also, even if we do look at cloud: Workspace isn’t bad (exception: sheets vs Excel), but SharePoint is the center of Teams, Power Platform, PowerBI… to replace M365 with Workspace means a lot of research, setup and testing of 3rd party alternatives to the above.

If you’ve ever worked in a well configured Microsoft stack, nothing beats the integration.

There’s no reason to believe Workspace would be more secure if it had the same feature set/integration configured.

Sheets is vastly superior to Excel for most users ;)

Most users don't produce most of the value.

That's actually good point, thank you. However not something that one can install on-premises or is "far cheaper".