If you're at the point of managing thousands of resources inside a single statefile, and that makes the most sense to your setup: you've outgrown terraform.
From my experience the problem at scale isn't that Terraform stops being useful. The problem is how state gets managed. Every IaC approach still has to coordinate changes across shared resources and none of them escape that. Other tools just shift the trade offs around. In house systems usually end up rebuilding the same thing in another form.
At scale the choices are pretty simple. You split state and live with orchestration glue. You move to a controller model and take on the operational overhead (see Crossplane). Or you keep a cohesive graph and fix the state layer. Those are the real options (imo). It's not about outgrowing Terraform.
From my experience the problem at scale isn't that Terraform stops being useful. The problem is how state gets managed. Every IaC approach still has to coordinate changes across shared resources and none of them escape that. Other tools just shift the trade offs around. In house systems usually end up rebuilding the same thing in another form.
At scale the choices are pretty simple. You split state and live with orchestration glue. You move to a controller model and take on the operational overhead (see Crossplane). Or you keep a cohesive graph and fix the state layer. Those are the real options (imo). It's not about outgrowing Terraform.