I've heard the same when the US forced MS to allow different browsers as default, when the EU mandated a common charging port for mobiles and again when they mandated USB-C. I've yet to see the groundbreaking innovation that I am missing in the smartphone charging area that was suppressed by EU regulation.

This again is a talked up hypothetical problem at best. We've had chat for 30y now and while progress has been disruptive in the beginning, things have considerably consolidated.

I don't quite get what's so great about having to install 5 different chat clients just because your social network is too varied to force them onto one.

It's a case of corporate greed where sensible solutions (like licensing out the protocol) are not done to damage the opponent. I don't profit from this - if companies hadn't been this evil, the EU wouldn't have come down on them. If they don't like it, they can just stop selling smartphones in Europe.