Hi Yao,
You did some very cool stuff here! 
in fact, you implemented your own curve blend! Yes, what you write about the too many spans is true, but sadly makes sense from the Dynamo point of view. So far, Dynamo works similar to Rhino (and probably a lot of other, non Class A CAD systems): whenever something needs to be re-approximated, they do it by simply adding degree 3 spans, until the needed tolerance is reached.
I also totally get that our Alias users shouldn’t have to re-implement the Alias math to get clean Nurbs tools in Dynamo (although, again, hats off for achieving that for curve blend!).
I will give my best to point out the importance of the availability of good Nurbs math in Dynamo to our product management team.