Ok - got it finally.
There is a litany of reasons why you cannot automatically place the anchor point in the middle of a text object. As you noted, the default location of the anchor point starts AT the Baseline of the first line of text. The math involved to calculate a midpoint is not worth the effort (and I have yet to actually work it out from within Motion).
That said, it can be done. It's a kind of slap your forehead kind of solution.
There is a setting in the Text > Layout inspector. Under Behavior Controls, there is an Anchor Point option. You will need to set it to All. The Anchor Position option needs to be set to Center. The Position parameter can be used to **offset** the anchor point from it's chosen Position option.
Doing this does NOT fix your problem. There's more to it. These options are called "Behavior Controls" and the text is not under behavior control at this point. You need to have a Sequence Text Behavior in order for this anchor point trick to work.
So — add a Sequence Text.
Now your problem is that the Behavior is designed to animate the text between two conditions. I'm relatively certain this is not something you want. So this is what you need to do:
Parameter > Add > Format > Rotation.
Sequencing : From
Animate : All
Spread : 0
The *secret* to making this a valid replacement for Transforms is to set the Start Offset to the number corresponding to the LAST FRAME of your Project. Specifically, if you have a 10 second project at 30 FPS, then you need to set Start Offset to 299 (if you have your projects set up to start at frame #0). You will also need to select the text object, go into Properties > Timing [Show] and set the Duration to 1 frame longer than your project, or in my example 301.
You can rotate but not animate with the Sequence Text set up as above, but you can animate rotations if you set the Sequence Text Start Offset to 0 and KEYFRAME the orientation of the text (even with Sequencing: From).
You can also animate the rotation from a Sequence Text using a Ramp behavior and use the Sequence Text > Rotation > X, Y or Z as the target parameter. The anchor point will continue to be honored.
[PS - while I was trying to write this I had to deal with a lot of distractions.... If you run into trouble or didn't understand something, get back with me -- I'll try to straighten things out. If this is the case, I apologize in advance.... gotta go.]