Very nice,
I do like the pot choice, and I do not feel it is too small for your tree. You will know if it is too small, you will find it will need watering more than once per day, that is a sure sign the pot is too small. If watering once per day, or once every other day is adequate, the pot size is just fine. I think some of Harunobu's impression comes from the angle of the camera to the tree. The area of the upper middle trunk that looks too thick, almost like reverse taper appears to be leaning toward the camera, so the optical illusion creates the image of reverse taper. Similar with pot size, the pot is further away from the camera than the middle of the tree, and so appears smaller than it really is. I think overall it is a good match of pot and tree. Nicely done.
If that is 'Wakaebisu', it is a nice and vigorous cultivar that should respond well to anything you do with it.