My non-heavily-researched understanding is that people who make their entire, or a majority of, their annual 'earnings' from capital gains may not be all that poor.
There's a whole spectrum of examples that can be used to demonstrate fairness or lack of fairness. Can you elaborate on your example of taxing a poor person even more by forcing a flat 30% tax on capital gains? Is this person you? What does your life entail whereby you are poor whilst also living almost entirely off capital gains?
You can still get all your capital out before the 1st of July 2027, and then re-distribute into areas that have better tax incentives, like new house builds. Sounds like that might solve two problems at once.
It's not me. I actually work for a living and I receive a salary. Many people I know with their own business plan to hopefully get out of it some day. They all make less than me but own a business of their own.
Let's say this works and those people who already have assets get taxed a bit more, when they are gone, there would then now very little incentive to work hard and start a business.
Such short term thinking will pretty much destroy the economy in the long term. You can't tax an economy to health and fairness.