As a native Korean, I can confirm that "각" is perceived as a single character. But the example itself is bad anyway because everyone use a precomposed form U+AC

As a native Korean, I can confirm that "각" is perceived as a single character. But the example itself is bad anyway because everyone use a precomposed form U+AC01 instead of U+1100 U+1161 U+11A8 instead (they are canonically equivalent). This is more clear when you also consider a compatibility representation "ㄱㅏㄱ" U+3131 U+314F U+3131, which is same to "각" after compatibility normalizations (NFKC or NFKD), but perceived as three atomic characters in general.