Fast action or a posed shot, the 70-200 f2.8 IS will get it for you with its extremely fast focusing. Some Canon glass, like the EF 85 f1.2 has a learning curve and requires thought to get good images but I think I could shoot with the 70-200 f2.8 while half asleep and still get good images. It will react to changing situations as quickly as you can which is part of what makes it such a killer lens for sports.
If I arrive at a sports event without the 70-200 2.8, I will have to conclude that I have lost my mind 🙂 These were some of the many shots I captured at a senior night basketball game last week with the EF 70-200 f2.8 and that lens and I will be back in the same gym Monday night for the first regional game.
Rodger
As always, much depends on what one photographs, under what conditions, for whatever output. I would say that the requirements in terms of gear for shooting an indoor backet ball game are quite different from those for say, bird or macro wildlife shooting. The focal lengths are very different - a basket ball court is a lot closer field compared to a baseball stadium, soccer stadium and certainly for birds and animals in the wild. So, it's always horses for courses. That is why I have a collection of different lenses and bodies for different scenarios - they are simply tools for a job.
For years I had the EF 70-200MkII L f/2.8 IS USM but because I don't need the weight since I don't shoot in such dark conditions, I was very happy to sell it and retain my EF 70-200MkII f/4 IS USM, as it is an excellent optic and much, much lighter. So, there are many elements at play here: light, distance, subject speed, ergonomics, output.
To answer the question about shooting in relatively low light. Certainly, the RF 24-240 offers versatility of focal range at the cost of aperture. That said, my experience has been that the dynamic range of FF R-series sensors is a step up from what was available in the DSLR world, so one can shoot at higher ISO values, and these days there is excellent noise reduction software available with most PP software packages - both of those offer some compensation for that and allow for such a super zoom to function with decent results.
In terms of low light performance, the two images I took of the Takahe, now in the Share your Images section, were actually both taken in deep shadow, hand-held, available light and are a reasonable expectation of what one might experience in the field. Given the narrow cone of capture, and the fact that both lenses had hoods on, reduced the impingement of light from brighter areas: and Takahe are not bright birds even if they are colourful.
