The assertion that a fee market only works if miners act as a cartel is false.  The situation in which miners do not act as a cartel simply presents the consumer with a range of prices which they can choose among, paying a premium if they are willing to pay for high-priority or prompt service or taking a discount for making low-priority or slow transactions.

Imagine a market in which there is no cartel.  To make it simple, suppose that there are ten miners each with ten percent of the hashing power, and that the block size limit is not routinely reached.  Because they are economically rational and facing different prices for bandwidth and electricity in their respective neighborhoods, they all set different minimum-fee policies.

The consumer is faced with ten different price points for a "minimum acceptable" fee, which determines how many of these miners would accept his or her transaction.  

So... paying a minimum fee would get your tx accepted by one miner.  On average you're going to have to wait ten blocks before that miner gets a block, so your expected tx time is about 100 minutes.  Paying a median fee would get your tx accepted by any of five miners.  On average you're going to have to wait two blocks before one of those five gets a block, so 20 minutes.  Paying the highest fee would get your tx into any block regardless of who mines it, so you'll be in the very next block in around 10 minutes.  

The point is that consumers are not faced with a binary "pay enough" or "don't pay anything" choice; they are faced instead with the opportunity to select a level of responsiveness desired and pay for the priority they want or need on a by-transaction basis.