> Clearly dividends or stock buybacks should not be costs. And thus such spending should only come from post tax money

It does. Dividends and stock buybacks are not tax deductiable [1][2].

[1] https://www.thetaxadviser.com/issues/2022/sep/paying-dividen...

[2] https://www.grantthornton.com/insights/alerts/tax/2024/flash...