An "uchi-mata" or "ankle pick" or whatever ... to that person becomes it's own martial art or "game" as people normally think of it.

There is incredible breadth to discover once you go 1 level deep into something. Every technique worth specializing in will have a multitude of entries/setups, then you need to know how people defend/counter and how to counter that, there could be slight variants that work better against different body types etc ... really staggering amounts of breadth/depth involved in putting someone on their back.

There will also be some breadth provided by general meta concerns of each combat sport like grip/hand fighting, defense, strategy, conditioning etc ...

So even the people who are hyper-specialized still have to know loads of stuff.