That is not quite it.
The US governmental system is designed to slow rapid progress, the methods of enacting change, outside of every single branch being packed with like-minded vanguardists - are incredibly slow and take years to even enact, and even longer for the actual change to come about.
Popular public dissent - directed toward different areas of the government speed things up rapidly - the public pressure shifts the power into the hands of the public away from the power brokers, so to speak. It is insane to think that voting could possibly move in the same direction as a protest - you vote every 2-4 years - unless you're a person that attends local council and board meetings. But labor stoppages, large scale marches, rioting, etc. all grease the wheel and can do things like rapidly establish labor rights, education rights, end de facto segregation, force municipalities to shift funding, end entire non-enumerated Congressional powers, etc.
Did you read all of my post? I said protesting AND voting is the way for forward for social justice. Try telling black folks from the 50s that their vote doesn't matter and they shouldn't care. They would slap the fukk out of you as they go to the polls. It is our duty as minorities to vote for candidates who at least acknowledge african american issues vs candidates who are virulent racist and wouldn't care if you got lynched.