Populism works since Caesar, and there wasn't Internet back then... Napoléon? Hitler and Mussolini? Do you know how it went in antic democratic Athen? Populism goes with democracy. Internet has nothing to do with it.
The society is more complex than ever? I read it at least twice: in a XVth century book, and in an antiquity one.
But this is beside the subject. You've said nothing here to explain why the reactionaries (the alt right, the far right, populism) are benefiting from this more than the left. Are you saying that the left can't win? Are you saying that we should shut down Internet?
You need to go farther in your analysis. There always were political forces opposing each other. The progressists were wining for women until recently. Why is it changing when young are so much more informed and educated than people were 50 years ago?