Hello, new member here. First of all, what an incredible resource this thread is. Many thanks to the OP for what's clearly a labor of love. If you've not had the chance, I highly recommend The Zaborin in Kutchan. It's a lovely hour or so train ride from Otaru and I think it could well be a contender for your top 10. We immensely enjoyed two nights there in Sept, '19. Very modern but hits all the essentials of a true luxury ryokan. Rooms amazing with indoor and outdoor onsens. Food incredible including amazing kaiseki and a very unique private irori experience. We also stayed at the Lake Akan establishment you reviewed above. Thoroughly enjoyed it, but fully agree with your take on some of the misses. Planning a trip for next year and looking forward to checking out some of your recommendations. Thank you!