I absolutely agree, RC Kyoto looks far more appealing (and unique) than StR Osaka, but per my previous post (you probably missed it while typing your reply), this is only about the last night, to ease the commute to KIX. While RC Kyoto remains 60k points per night, I'm all in - it's a steal on points. Just debating over what to do about the commute the next morning, and Mrs JK not being too helpful in terms of providing opinions or preferences (no doubt she'll chime in once it's all booked and irreversible!)
There really is not that big of a difference, as KIX is also not that close to St.R Osaka. So, by train I would absolutely just do it from Kyoto assuming your flight is at a reasonable hour. If it is a ridiculously early flight, I would actually suggest leaving for the airport the night before and staying at an airport hotel. I hate traveling to airports in the early morning if I can avoid it.
Moving to St. R would be more of a hassle, and that would negate any marginal time savings to the airport the next day. Really not worth it.