The new Channel Animation format does not use TweenService at all. As a matter of fact, we have even retired Bounce and Elastic easings and they are not available for that format (they are still available for KeyframeSequence animations, though!).
Instead, we only rely on constant, linear, and cubic segments between two successive keys. However, we added tools to generate cubic curves that match the Bounce and Elastic easings, but those tools are only available in the Curve Editor, so animators can still create the same kind of animations they are familiar with.
For your specific use case, I think I would keep the current implementation. Setting up two RotationCurveKeys within a RotationCurve within a CurveAnimation would carry quite a lot of overhead for a relatively simple interpolation between two CFrames.