Well, I simply wanted to clarify what you presented in a way which seemed to me to be causing more confustion to OP in this context than necessary.

Basically this was the problem for me:

don’t forget that focal length also affects light transmission. A longer focal length gathers light from a smaller area of the scene and therefore less light than a shorter focal length.

In the context of format comparison, it can get confusing to the OP as in this context the focal lengths collect light from the same area of the scene, not different.

Thus, it answers OP’s real question about why exposure isn’t changing even when the entrance pupil diameter changes

We interpreted OP’s question differently. Not saying either interpretion is better or worse.