Perhaps, but it is not always the case. I did some work for a big bank, and some people were producing absolutely terrible code (and all the other coders knew it), despite passing a rather rigorous interview test.

In general, I think that merging lists and similar tests that are not much more difficult than Fizz Buzz are fine, but any harder than that doesn't seem to be worth it.

I know this is not answering your question, but Google Drive already does for me most of what your app would do. I haven't attempted some of the more advanced features that you are aiming for, so it is possible that those can be worked in as well. Also, I despise Excel, and I can't be alone there. Not to say that you shouldn't write the app, just that you may want to think about this alternative work flow, at least as a source of ideas.