The closest we can reach for “tenant key” based single database multi-tenant app with frappe framework is with a “tenant” doctype link field on each document created by app and user permission set to “tenant” doctype.
I feel Workflow fits well where there is low-code, no-code scenario for end users to set it up quickly from web ui. May be add some minimal tweaks from scripts.
If you try to force thing on to Workflow you’ll have to handle many cases and add that to upgrade and maintenance overhead. Workflow actions are being created for every user