Huh. A good example of why Wikipedia cannot always be trusted. I am not able to verify the [1] and [2] citations.
To get back to the topic at hand, Tonkatsu is definitely at least as “traditional” as gyu-katsu and definitely much more so than chicken katsu. I would love to try Chef Schlosser’s (or Chef @JLee’s!) tonkatsu.
More on tonkatsu:
Most people on this board are fans of Kagura, but my personal favorite is Komatsu. Their Hamburg Steak with demi glace is also 
.