griong Hi
You're right, we have 2 builder tools at this moment, JA Builder + T4 Builder. You might already read my explanation for the difference between these 2 tools, JA Builder is the older one. When we develop our new Joomla Framework called T4, our team want to have a new builder as well, with a new approach and the new T4 Builder is released.
Both JA Builder + T4 Builder are kind of Joomla components, it's not a MUST to use one of them with any framework so of course, they both support T4 framework (as you may know, the framework is used to develop Joomla templates, not builder).
At the first stage, we'd like to focus on T4 Builder but there are high demand from our customers to update JA Builder to Joomla 4 / Joomla 5 so we continue updating JA Builder to Joomla 5. That's why we have 2 builders at this moment 🙂
I also replied another topics from you 🙂