What a strong CodeIgniter specialist actually knows
CodeIgniter is small and quick, which is why so many business systems still run on it. A good developer knows the difference between versions 3 and 4, writes proper models and libraries instead of stuffing controllers, and uses query builder safely so injection is never a worry.
They add what the framework leaves to you: structured validation, token authentication for APIs, caching and tests with PHPUnit. They also know when a system has outgrown the framework and say so honestly.