It's not black and white. For fast primes for example IBIS is far superior for the simple reason that lens stabilization is often too difficult to make (and it is always a slight compromise in terms of IQ). Up to around 100-200mm I'd say the best IBIS systems are as good, or better given they have more degrees of freedom, as lens IS and after that lens stabilization is simply superior. That said I do not have extensive experience with FF cameras with IBIS so it could very well be the crossover point comes at a shorter focal length.Having said all that most tests I've seen do seem to suggest that in lens IS is superior. Nikons F-mount 24-70 VR for example stabilises better than their new Z mount 24-70 relying on IBIS. Of course some are now combining the two and apparently that brings great benefits but we will have to see how it pans out.
But not only. You can shoot landscapes with a 400mm if you want for example, those don't usually move much.I was thinking in terms of the subjects. 400 mm primarily used for wildlife, birds and sports. I suppose for a large slow moving mammal at rest or a bird sitting in a tree you might be able to shoot at 1/50 of a second, but that's not generally my experience.