Yeah Robo-Samurai was not a big problem for me in the end because it had CBM logic and had the purpose of being a life support machine and built to take Logans powers from him, it made sense, as you say.
But I would have liked to have seen one fight with the traditional armor, even if when Logan has that short dream/nightmare about it, that would have been really cool, and also the way they went it kind of meant Harada ended up being a bit of a loose part and his character was wasted, literally.
However I have thought on this and I guess the makers thought there was no point in setting up an SS character in the long term as they always said this is a one off story and so if it had been a normal SS from the comics he may never have been used again so whats the point!