I agree it had a part in it, but its not the whole story. Its the citizens being unable to elect people not beholden to political parties, with party obligations. These obligations appear to be more important than their obligations to the people who put them there.
This isn't a Citizen's United issue as much as it is a set of political parties that have evolved to control their captive populations. Some people vote D|R precisely to stick it to the others. They don't care about representation. They care about tribalism. The parties foster and encourage that thinking. The various "news" channels have their own opinions and often align with a particular party. Which means they are in the propaganda and red meat business. Not the news business.
CU is a part of this, in terms of providing fuel for the fire, but its been going on much longer than CU, and will continue regardless of whether or not CU gets struck down going forward.