But I am pretty sure every economist agrees that a wealth tax doesn't make any sense mathematically
I find it difficult to believe you could come to this conclusion in good faith, given how many serious economists advocate for wealth tax.
This economist wrote an award winning book on the topic https://en.wikipedia.org/wiki/Capital_in_the_Twenty-First_Century, where he advocates for a wealth tax.
Assuming he pays 25% tax, which i'd be very suspicious about, he's about 2 million short of his current "fair share".
26 000 000 * 0.25 = 6 500 000
26 000 000 * 0.33 = 8 580 000
If he's deferring till retirement, then likely his tax rate is less, and the bank is lending him money which he can spend freely and call a capital loss lowering his effective tax rate when he does incur those taxes.
The thing about being this wealthy is you can afford to pay people to find ways to lower this rate.
I don't think i'm "mad" about this, but concerned. This kind of inequality leads to violent upheaval, and is currently the cause of a whole pile of unnecessary suffering. If we didn't have people that were this wealthy and some of that money was distributed to say education, healthcare, UBI, we could all have a much healthier pleasant life.