No, of course the dude in the viking outfit wasn't going to single-handedly overthrow the government. There was a very real possibility that members of Congress would have been murdered for political reasons by a very large, violent, deadly crowd.
That doesn't really matter, does it? Isn't it like criminal conspiracy where all that really matters is for at least two people to plan a crime? AFAIK it doesn't matter if the plan is bad, there just needs to be a plan.
Was this a well thought out plan? No. But would it have been enough to derail the process of formally choosing the next President? Quite possibly.
That was their clear goal. It has been for months, and Trump himself has been saying as much in no uncertain terms. They were looking to intimidate, possible kidnap or kill, members of congress and the Vice President in order to prevent the results of the election from being confirmed.
It's easy to get political fatigue in the current climate, I understand the knee-jerk impulse to assume "hey, you're probably overreacting about this political issue". But some things really are a big deal. Like overturning an election.
Step back for a moment and ask yourself honestly: do you really believe, in your heart of hearts, that there was even the slightest, faintest, remotest chance of the dude in the viking outfit overthrowing the US government?
It was a violent protest that got way out of hand, absolutely. There was never even the slightest chance of the government being overthrown though. It's like someone dropped a cigarette butt on the ground and people are leaping on the opportunity to call it attempted arson.