So you're completely ignoring the rise of fascism due to voting? The second world war happened because a bunch of nazis stormed the German parliament and took control of it by force? What do you think populism does?

Of course you can change the system from within. Le Pen, Höcke, Meloni, Wilders, Trump, and so on, they aren't "part of the establishment". They latched onto a populist narratives, got financial aid from the radicals in their countries, and gathered votes to get themselves into offices .

The left-wing parties in France united to pose a unified front against the national assembly (le RN) in France. And it worked. They got the relative majority to vote for them, but as soon as they won, they were beset by infighting. Such is the common reality of left wing parties - they are their own greatest enemy.

Either you chose to ignore it or you were unaware, but the latter is much less probable, so I'm going to say you chose to in order to fit your narrative of "voting doesn't matter" and imagine that class warfare (or how Marx would put it "Klassenkampf") is the only way out.