You can learn to use your mind in ways that make you more happy. You can learn to use your mind in a way that you are more grateful. Just because you haven't doesn't mean you can claim that no-one can do this.

You then use a biological condition 'cancer' to try to make the point that we can't change our emotions. Our emotions are not the same as our biology. It's easier to control your emotions with the right patterns and processes than it is to reverse genetics and control biology.

You seem to be on your high horse. The abundance mindset is a real mental change you can make in which you change the lens you see the world through as one with more opportunity. A new perspective does not mean illusion. Much like someone else might look at a problem you have and be able to provide advice or insight that you had not previously thought of. Their standpoint was not imaginary, it just wasn't one that you held. Similarly, if you can change your natural vantage point towards problems in life and opportunity in your life - you can take up a new energy and attitude in general. I know firsthand and have watched others do the same, don't tell me it can't be done.

There will always be people who have grown and evolved into peaceful abundant mindset. And then there will always be another group throwing stones saying it is woo woo and impossible. I hate to be cliché, and I know this will trigger some. But which pill do you want to take.