That’s been a sticking point for us as well- just so you’re aware, the Webflow team is very aware of it, but of course it’s a significant engineering challenge.
The approach I proposed is to allow a workspace to guest-invite an Agency account directly, rather than guest-inviting only individual users who are in Agency / Freelancer accounts.
One challenge to this is that ideally it would be a multi-part chain. My Agency A often does work for other Agencies B who work in their client’s workspaces C. That’s a 3 workspace chain, and ideally, C invites B, and B invites A. This gives B the ability manage which users ( and invited agencies / freelancers ) have access to C’s project(s), with control over Site-Specific Access (SSA).
A lot of engineering, but it would enable such an incredible eco-system of freelancers and agencies. Almost like having a built-in skills marketplace.