The PH Kyoto does not have an onsen.

Central Kyoto is not an onsen area. You can't just create an onsen just because you want one. And it is obviously not possible to run several km of pipe or even longer to get access to the nearest onsen source. There are only a small number of hotels in central Kyoto that do have an onsen, none of them even mid-level properties,

Nor is there a large public bath at PH. But of course neither the RC nor the FS has a large public bath either.

I think the best one could hope for at the PH would be rooms with a nice hinoki bathtub with a view of a bit of garden, but that is not likely in the base level rooms.