Amazon can in fact take their grocery business to zero profit safely, trivially. That includes taking Whole Foods down to near zero operating profit levels.
It's the ideal approach and classic Bezos. Their competitors can't afford to match it in the hyper low margin grocery business. Walmart can try, however their profits have already been badly squeezed downward for the last five or six years in a row now, in competition with Amazon.
Kroger, a $121 billion sales giant, has a mere 2% operating income margin. Amazon can tip them over and kill them very easily by eliminating that small remaining margin. Kroger effectively has zero margin of safety in their business, they can't afford even the smallest of drawn out price wars with Amazon. Kroger also has little safety buffer in their balance sheet, barely positive in assets and a small sliver of cash; while Amazon has $37 billion in cash. Bet on a Kroger bankruptcy or forced sale in the coming decade, pinned between Amazon and Walmart.
AWS is set to be a ~$15 billion per year profit juggernaut five years out. Their ad business is going to generate a minimum of $8 billion in profit at that point.
They can very easily bury the entire US grocery industry at zero margin to pursue aggressive market consolidation (the grocery market is extremely fractured). There is no other means for them to compete in groceries other than for Amazon to take the margin down to a level where they drown everyone else in their path, while not having to worry because of their profit offsets in the rest of the business.
Predatory pricing is not a concern in this scenario. Walmart has always done exactly the same thing in subsidizing one part of their business with another depending on where they're looking to expand market share. They've rarely had a problem with regulators over it.