I previously deployed stuff to Salesforce when I ran a very large Asia-Pacific Salesforce org.

The previous way (prior to SFDX which was clearly influenced by Heroku) was terrible. 12 hour long deploys that end when one unit test times out-style terrible. No code history terrible. There is no way that Heroku was worse for integration.

Whether they could have replaced APEX with Heroku is a different issue.