Bonds only give you certainty to the extent that inflation remains certain.

Stocks generally rise with inflation, whereas bonds continue paying out the same nominal amount, which buys you less over time.

As a retiree I'm 50/45/5 in stocks/bonds/cash, having opted for a conservative portfolio. The stocks are the only reason I haven't lost buying power. But the bonds have performed so poorly that I've barely kept up with inflation despite the amazing bull run in stocks.

Are we talking about bonds or government bonds here? The former will beat inflations assuming you don't just buy AAA rated ones. Investment grade perpetual bonds in US dollars yield over 6.5% on a Yield-to-call basis.