What do you think about code being too smart for current team? I encountered that use-case three times in my career. It was C++ program which was written by very bright person, used template magic, boost and stuff. Rest of the team were ordinary C developers. After that person left, they had to rewrite his program, because it took too much time to understand how it works and to fix or improve it. Second case was when someone wrote some helper program with Haskell which happened to be important. Same story, nobody knew Haskell, nobody wanted to invest into learning, so rewrote in node.js. Third story: someone used reactive API with Java (Spring Flux) and again same story: team don't understand it and slowly rewrote it with ordinary blocking API.

Does that code counts as legacy?