> When applied, Terraform code would spin up a template of what the service should look like by creating an ECS task set with zero instances. Then, the developer would need to deploy the service and clone this template task set [and do a bunch of manual things]

> This meant that something as simple as adding an environment variable required writing and applying Terraform, then running a deploy

This sounds less like a problem with ECS and more like an overcomplication in how they were using terraform + ECS to manage their deployments.

I get the generating templates part for verification prior to live deploys. But this seems... dunno.