No they're arguing Super PACs distort and limit healthy, democratic speech; that Super PACs are detrimental to speech.
The corollary to your assertion is that Super PACs increase speech. But this 'increased speech' can similarly be 'increased' by foreign political donations, which highlights the absurdity of these 'speech' claims to anyone interested in reclaiming a properly functioning democracy.
Lessig gives specific examples of possible policies to illustrate that it's actually an increase in speech rather than a decrease in it, here: https://mayday.us/the-plan/#fundamental-reform-in-the-way-el...
People are not equal and we need to recognize that; some are famous - their speech is hear by more people than mine, some are rich, some are well connected, some are beautiful, some own a newspaper, etc. Not everyone has the same voice, and that's ok.
If money is speech, especially with regard to politics, lack of money is the stifling of speech (and to an extent, indirect disenfranchisement). Ergo, through not giving those without money any funds with which to perform their speech, the government is violating the first amendment.
This reducto ad absurdium is meant to illustrate that money, while necessary for a bullhorn, is not speech in and of itself.
The only way to implement any solution - whatever solution you think is needed - is to implement Lessig's solution first.
The correct solution is to decentralize power; it easier to win one election instead of 50. And to reduce the amount of activity the government does, less pork spending and less market distortions.