Emotionally, the humans work in the new films because you see them grappling with their impending demise. So, you might be asking, why do talking humans work well in these new Planet of the Apes movies? Well, it's because we have an expectation to see humans that act like us since the planet of apes is just beginning. People don't want to see a film full of talking humans as the main characters if the film is supposed to be about a world of talking apes. But again, the title of the film is Planet of the Apes. Perhaps Burton thought this decision would make the humans more endearing, which would make the audience more invested.
They're talking humans like you and me, who were captured from their communities in the wilderness by apes to become servants to the ape upper class. Most of the characterization is extended towards the humans, who, while captive like the humans from the original Apes films, aren't the animals we were expecting. Instead of focusing solely on the apes, the apes are instead treated like special effects instead of well-rounded characters.
