The prices might very well stick.
https://www.cnbc.com/2017/08/24/amaz...aboolainternal
Amazon runs on a reportable net margin of 1.7% whereas Whole Foods ran at 4.6% as an independent company. If they cut their margins in half they'd still be higher than the Amazon average.
They have room to cut and still thrive now that they're not under Wall Street pressure.
They'll never be the cheapest of the cheap, though. Organic stuff is simply pricey.