Broken record here, but Bard doesn't replace your Archer. They are two separate things. The system doesn't dictate that you must become a Bard if you have ranked Archer to 50.

You are still an Archer. You just have the option to use Bard as a separate profession. Which is actually an upgrade in my opinion. You have the awesome DD capabilities with your Archer class and a support job. What other classes get that kind of treatment? You are basically being stretched into more desirable roles. I think Archer prereq for Bard is getting more bang for your character progression.