The reason that the animator controller constructed in the editor works is : When starting PlayMode, the transform bindings are created before the unity event system and the value of the component matches the constant value.
The reason that the playable constructed at runtime does not work is : When starting PlayMode, the physics loop go before the animation loops, which changes the component rotation data (confirmed using data breakpoints). This makes the above code think that there is a mismatch between the component and the constant value, which will consider all further bindings as non constant.

A new Advanced option was created for the animator to make sure we can shoose if we want to optimize constant curves or not