>> Kinsuikan vs Grand Hotel Arimoto -- the Arimoto looked less traditional to me, but ...

Am mildly objecting to the "but". I would call both of them ryokan hotels. They both have J-style rooms with the elements of a traditional ryokan room (tokonoma, hiroen, tatami floors, zaisu and low table, futon for sleeping). Both have J/W-style rooms and at least one has a full-on W-style room (sofa, Western bed).

One photo of Kinsuikan had a perfect photo of a traditional ryokan room - except for the little sofa and recliner chair in the hiroen (veranda) where I would expect to see a small table and two chairs. That is "less traditional" which is not a knock. For this solo traveler the recliner looks like a nice feature. Being less traditional is not any kind of compromise, imo.

To choose, the cost and room amenities are important considerations, but I would be more interested in the meal options and the location. They will have a standard kaiseki dinner but likely have some more deluxe options/variations. I assume that they both would serve dinner in restaurant but maybe one will serve it in your room. I assume both would pick you up at the port but would be nice to have a shuttle to get around if the location is more remote.