That’s the whole point, when you do useless shit like buying from one corpo instead of another, they only need to buy couple of politicians to succeed. The only way for you to combat it is to elect politicians they can’t buy and apply political pressure to the rest of them, so they can’t buy them all. If instead of that you play their game and try to outbuy a corpo that owns half of your country already, not only you will lose every time, you are actually doing exactly they want you to do.
“No ethical consumption under capitalism” is about this, not anything else.