The thing is, it's not just apples and oranges. Let's say that real world serious violent encounters are oranges. Now, there are a range of oranges; navels, temples, juicing oranges, and then some that people tend to forget about and misidentify, like tangerines, satsuma... An orange is not just one thing.
Now, some sport combat is definitely apples. I would say hard contact but range limited sports like Boxing, BJJ, Kickboxing, WTF TKD, Kyokushin, etc, are all apples, whether Braeburn, McIntosh, Jazz, Gala, Honey Crisp, or Golden Delicious. If all you've ever eaten is apples, your first orange might surprise you when you you bite into the skin and it's bitter and tough, or when you find segments with seeds rather than a core. However, it's still a spherical fruit with skin, a stem, seeds, and edible flesh, and it still grows on a tree, and there's a good chance you'll still figure out you can pick it, and how to eat it. You just might have some unpleasant surprises on the way.
Some sports, like point sparring, no contact sparring, (and probably some others, I'm not as familiar here), honestly, are probably more like I dunno, lettuce. Again, there's Romaine, Green Leaf, Red Leaf, Escarole, Friseé, but it's all leafy greens. If you eat mainly Boston Butter Lettuce, you'll probably be pretty good at figuring out what to do with dandelion greens or collards even if you've never seen them before, but oranges are going to through you for a loop. There's a good chance you're going to eat the leaves of the tree, rather than the fruit. You might figure it out, you might not. That thick peal is definitely going to pose a challenge.
Some sports and arts, on the other hand, when well trained, are not apples or lettuce. Things like MMA. Things like most traditional arts trained for civilian defense. RBSD. They're not oranges either. They're, Lemons, Limes, Grapefruit, Pommelos and Ugli Fruit. They have that same thick bitter skin, they have that same sweet-sour flesh, divided into segments with seeds, they have pulp, they grow on similar trees... Sure, if you've only ever eaten Grapefruit, oranges might disappoint you with their more simple flavour, they skin might be a bit harder to get through than you expected, it might take significantly less time to eat them than you might be used to. But at the end of the day, a Grapefruit and an orange are relatively good approximations of one another. They are not and will never be the same, but they're pretty close.
On the other hand, if you cut an orange in half, bisecting the segments, put it in a bowl, and try to eat it with a spoon, well, good luck with that.