The Matrix by itself is just a group of a few vectors. The first three describe the position, and the other nine define each time three vectors with three "sub-vectors". All of that is ist based on the length of these 12 vectors. The Matrix has no concept of Head, Pan, and Bank (HPB)
The Standard Null Object has, for simplicity, to use it.
The channels in the Timeline are not labeled to reflect that, as it would be confusing when the Rotation order would change, and then the naming and all values would need to be changed. That is not a given.
Perhaps check with Tech Support, to get a second opinion, if consider that a problem or not how it should be.
The node system is, so far, my impression, more of a developer platform for capsules and such. Solid knowledge like HBP v Matrix and why rotation order matters are expected. Again, that is my personal view.
All the best