Cheeky Visual - It's not all about Yield!
It depends what the business objective is and the Bean Counters in Donington Hall will decide this. Most LCC's have a Volume based model when compared with the likes of Eastern Airways or VLM for example. Those that sit on the middle are generally the airlines with no clear strategy are generally the ones that end up belly up.
Whether an airline or route is or indeed isn't profitable depends on overall revenue whether this is achieved through High LF/Low Yield or High Yield/Low LF. This is not done at a route level, this is sometimes even at a flight number level where demand varies.
It's not as straight forward as it first sounds, there's a science behind it.