You proceed from the assumption that there's a problem and we have to worry about it. As you yourself said, we've seen a tectonic shift, to use your words, and you have a huge number of sources of information right now, something we hadn't... Yes, we have a great concentration of ownership, but does that reflect itself in a homogeneity of voices? That's a big question.
As you well know, your kids, as you say, much prefer their iPhones, and their iPhones may be from Rogers or Bell or one of the three big companies, but the content they get, the access over that iPhone, comes from all over the world, from all over Canada, etc.
So yes, the means of access are owned by three companies or four, however many you want to consider, but it doesn't necessarily mean the content is the same and that you therefore have problems and not a diversity of voices.