They are completely different products just reusing branding to confuse what people are asking for.
RHEL Developer is closer, as a no-support, no-cost version of RHEL, but you still have the deal with the licence song and dance.
CentOS gave folks a free version that let you run some dev environments that mostly mirrors prod, without worrying about licences or support. CentOS stream doesn't do this out of principle. It's upstream.
To call it "completely different" is false. They are built differently, but the end result is still 90-95% the same software versions (because it has to be as the major version of RHEL). In fact, the way it is built differently is a massive improvement over the old process. The old CentOS was put together by 2-4 people at a time, with long delays after the corresponding RHEL releases, with no ability to actually fix bugs or accept contributions. The new CentOS (CentOS Stream) is built by thousands of engineers, literal subject matter experts who can actually fix bugs you report to them, or even better merge a contribution you submit. Also, the branding wasn't reused, the branding is for the whole CentOS Project, which still exists and is more active than ever. Also, you can still use CentOS in your dev environments, and it works great for that because you can prepare your production workload for upcoming changes in the next RHEL minor version ahead of time. You can also get free RHEL for dev environments, for the things you need to validate with the same minor version as your production RHEL environments.
They are completely different products just reusing branding to confuse what people are asking for.
RHEL Developer is closer, as a no-support, no-cost version of RHEL, but you still have the deal with the licence song and dance.
CentOS gave folks a free version that let you run some dev environments that mostly mirrors prod, without worrying about licences or support. CentOS stream doesn't do this out of principle. It's upstream.