It's impossible to know yield data for every city pair, so I guess demanding that level of info allows anyone to believe that their opinion is fact...

Some examples - not yield but average fare (same thing, just divide by stage length to get yield:

LAS/SNA = WN $126, US $112
LAS/LAX = WN $117, US $110
LAS/SAN = WN $115, US $107
LAS/PHX = WN $114, US $113

Some longer flights - over 500 miles:

PHX/SLC = WN $153, $US 143
CLT/NYC = B6 $127, US $152
PHX/SMF = WN $172, US $164
PHX/SJC = WN $159, US $157

Even longer - over 1000 miles:

PHL/PBI = WN $145, US $183
PHX/MCI = WN $235, US $196
PHX/OMA = WN $180, US $166
PHX/CMH = WN $202, US $216

I could go to longer segments, but without looking up connecting vs non-stop I didn't want to confuse things (even some of those above may differ).

If one wanted to go to the trouble, table 6 of the Air Fare Report gives all city pairs with over 10 passengers/day so one could select comparable flights (non-stop, 1 or 2 connections) and compare fares. The only trouble is that only two carriers are given for each city pair - the one with the largest market share and the one with the lowest average fare. So city pairs where two carriers compete directly may not list both of those carriers.

Of course, another big complication is that nearly all tickets are sold at prices set by the airline, not by the customer. So what a particular customer may be willing to pay and what they actually pay can be two different amounts.

Jim

ps - RASM won't help you compare what customers do pay since it incorporates load factor as well as yield.