I'm genuinely curious, if you have a 70-200, why not just get a 15-35 and 24-70/28-70 aswell to cover the focal lengths as you said yourself this lens is useless in low light.
By comparison, the 24-240 is inexpensive and becomes a great single"walk-around" lens when you don't want to carry a bunch of lenses or you don't want to take time to change lenses for a spur of the moment shot. Basically, it is for a different shooting situation, much as even a classic 2.8L zoom lens can't compete with a good prime.
What I love about the 24-240 that is is very predictable what you are going to get and it is very sharp in the center even wide open at any focal length.
BTW, I was already planning on getting either the RF15-35f2.8L (which I have since bought) or the (rumored) RF14-35f4L. I have also ordered a refurbished RF24-70f2.8L. I don't plan on getting a 70-200 as I think the 24-270 will do for my needs. I might think about the 100-500 someday.
What I don't fully appreciate is why it is being discounted so much these days. It suggests that the lens is not as popular as I think it should be. Similarly, the RP is being discounted. It could mean that more pro/high-end shooters buying into the RF system, but not more average camera enthusiasts.