With the very greatest of respect, you are confusing cost and price.
Low cost is about the airline establishing a cost leadership position, such as Ryanair.
What it does on pricing fares is a different matter.
You may notice that Ryanair advertises itself as ‘the low fares airline’, not ‘the low cost airline.’
Revenues minus costs = profit 🙂
You are absolutely right in your comments about obtaining best value and that will often not come from the low cost airlines.