Steve
Mostly Harmless
Unless a specific study is done, it's hard to say whether it's more or less efficient. I mean, if someone wants to be an elite level MMA fighter, is it more efficient for him or her to train in an MMA gym out of the gate, splitting time between grappling and striking, or to start with wrestling, then add BJJ, then add striking, and then synthesize the discrete skillsets? Is one clearly better than the other? Both methods produce elite level competitors.So I think that first part depends, and not sure if we can get a direct answer for that, beyond specific individuals. Overall, I think professional boxers are probably more competitive than most people, so they may be more likely to train for competitions, but at the same time I can see them view it as simply a tool, and not care about competing with it. So different boxers different answers.
As for the athlete thing-I don't really know what point you're making with that. The fact that some people can/do switch between them, doesn't mean it's the most effective route to do it. And with MMA and BJJ I think that might be an exception to the idea, considering just how similar they are-nearly 100% of BJJ can be transferred directly into MMA, so for one-direction there is nothing being lost. And then there are other people who aren't high-level BJJers (meaning they don't enter high-level BJJ comps) that are high level MMA fighters that are also successful, so it doesn't suggest one method is more effective than the other.