I finally made a video.
Gameplay on second highest difficult. No edits, cuts or pauses.
There is a part 2 of the video also with the last matches.
I started with a 3 button controller but later changed to the normal 2 button. The 2 button controller works better than you might think. Changing between kick and punch takes a little of course (change with the select button, or set it to start) but when I played against Honda I started to do it somewhat succesfully. For me it didn't detract much from the gameplay actually. I have a played a lot of this game on SNES and the pc engine version is not far behind it even with the crippled controller. It may be slightly easier too, although it is hard to say, but the opponents seem a little stupider in this pc engine version.
In any case, I have fun with this game. You probably only need two buttons to play it.