Regarding individual action, being vegan is likely the most effective thing one can do to reduce ones own emissions (except if you're a frequent flyer, then stop flying). Yes, that's under the assumption that individual action induces change. But that would also be arguing against switching to bikes, using public transport, and less flying.
You're completely right that we need systemic change. And to get there, protesting, direct action, civil disobedience are likely the best we can do and far more effective than individual changes. But these actions also only become effective once there is an actual systemic shift.
Yes it does. But that's not due to vegans, is it?