"build on top of existing, well-defined codebases/APIs." is not necessarily easier than "engineer a complete, well-rounded, extensible codebase/API himself." I

"build on top of existing, well-defined codebases/APIs." is not necessarily easier than "engineer a complete, well-rounded, extensible codebase/API himself." I think these are two different skills. Some programmers are better in building on top of existing codebases, some programmers are better in build things from scratch. maintaining vs starting.