Yeah but in this case the diversity is a weakness. You can't replace Yahoo! because they don't do one thing really well, they do a bunch of things mediocrely well. What is the Yahoo! brand? What do they do anymore? No one really knows, even though they do a ton, so how could you even aim to replace them at all? At best you could aim to replace Yahoo mail, and that seems like a very reasonable (though still ambitious) startup goal.
Unless you plan to simultaneously disrupt web email, search, financial portals, sports, news, generalized all purpose portals, and on and on.