Donating a 10th of your net worth in less than a year is huge. And it only offsets her taxes by as much as she donated. Best case scenario is she sold stocks, made a profit of $3.8 billion or less, and then didn’t pay any income taxes on those stocks. But either she was awarded those stocks and taxes would have been paid taxes when she received them (meaning, even if she didn’t pay the taxes herself, that she would have less total money now) or she bought them cheap and sold high, meaning more of the total amount is profit.
So even if she didn’t get taxed on the $200k she lived on that year, taxes for that $200k still would have been paid on the assets already.
The only exception for this is basically for income-like money that is in the lower tax brackets, which is an advantage that most people have and that impacts lower-income people a lot more in terms of total percentage of taxes paid.
If every billionaire donated 10% of their net worth each year to worthy causes, we’d be in a much better place. Not as good a place as if we didn’t have billionaires in the first place, but that’s not because of the billionaires - it’s because of the system that allows them to exist in the first place.
She’s also pledged to donate a full 50% of her net worth. That’s far more than she could ever benefit from in tax breaks.