Today, there are several levels to manage variables in Octopus, and it's a good thing:
- Library variable sets
- Project variables
- Tenant variables (thanks to variable templates)

I think you should really simplify this process to manage all of them from Library variable sets only. Indeed, when you create a variable from this section, you can link it to some environments, some targets, and some target roles. If you add the possibility to link it to tenants and projects, it's win :)

Doing that would also allowing to set tenant/project variables only to some environments, that is not possible today.