Either your colleagues were very misinformed, or this was a slight misunderstanding on your part: Terraform IS cloud agnostic, but not in the way you understood.

Instead, it allows you to use the same tool and management model for resources on any of the 3 big cloud providers, about a 100 assorted SaaS providers, and most importantly, wire them together (e.g. create a Mailgun configuration, and set up its verification DNS records on AWS), all in code, and in the same workflow.