That's the same old Tragedy of the Commons argument, which is valid no matter if we're screwed or have a decent chance at solving the crisis. Using this logic, it's irrational to even vote since you waste your time on something which with all probability will have 0 effect.
> Systemic change is what matters
That's true, but how do you get a systemic change? By influencing individual voting and consumption behavior. Global warming has been started and is still driven the most by democratic countries, you can't absolve yourself of the responsibility.
Corporations are a product of the system we've built. They'll never care about the environment, they're not designed to do that. They care about the legal framework, though, which we (in democratic countries) can influence. The hard pill to swallow is that forcing corporations to care about the environment will increase their costs and thus prices of goods and services.