Infrastructure is not our primary focus. We consider ourselves to be infrastructure light. Meaning we do infrastructure as a means to an end and it isn't something we specialize in beyond those needs. We have no interest in contracting to just do infrastructure work for anyone.
If a client has an existing team with DevOps people that manage the infrastructure we will happily work with them. If the client doesn't have such people then we put on our infrastructure hats and evaluate the needs and decide between two approaches.
If Heroku is fitting for the project then we will default to that. If the project requires more control over the infrastructure for whatever reason then we use AWS managed via Terraform and Kubernetes.