It's easy to make those points but maybe less easy to prove them. Is the grocery market really distorted?
OK, a couple of examples:
1. Company A supplies product to supermarket X. They get a call one day saying if they want to continue to supply to X they have to drop all their other customers.
2. Company B is supplying product to supermarket Y. Periodically, they are told they must supply that product, at below the cost of B's production, so that Y can offer it as a promotion.
Do you think that these are market distortions and the supplier is simply free to go elsewhere? Keep in mind that the concentration of market power in a very few large retailers means there's little in the way of options to sell to an independent wholesale market.
The facts suggest otherwise:
1. There are more big players in the retail sector than ever before.
2. Farming & food production are booming, despite an economic recession.
3. Most of our food product is exported while most of our food consumption is imported.
So our producers are far less dependent on domestic supermarket chains than they were say 20 years ago.
Where's the problem?
Your facts are of limited relevance. Yes, most produce is exported because it is focussed in a small number of areas (beef etc.), and we simply couldn't consume the amount produced. Yes, production in some (export-led) sectors is booming, based on increases in global food prices. The exact numbers of big players fluctuates, but their combined market dominance continues to increase.
The supermarket's PR machines have done a good job if people think all is rosy and we're well served by a competitive market. It's so much easier to indulge in some headline grabbing promotions than have some real competition.
If all was well with competition, one would expect prices to lower and align with other markets: the fact is margins are much higher here. Of course, it's next to impossible to find out what they actually are at a detailed level; as the supermarkets would say: move along here, nothing to see......