There is no simple answer and I think you meant, CASM!
A 747 has a lower CASM than an 88! However, that means little if the seats can't be filled with passengers purchasing tickets with a good average yield. The 747 has the "potential" to make more money than an 88, but it also has the potential to lose more money.
The example holds true for a 70/90 versus an 88. There is "potential" to make more money with the 88, but also there is a potential to lose more money in an 88. But, there is also the "potential" to make more money with a 70/90, than with an 88. There are many factors that can determine which airframe is the best match for a given market. Each type aircraft is a tool and the idea is to right-size the tool for the job. This goes to prove that size does matter--the right size!
You are correct, but there is something that need to be discussed. The 70/90 seat platforms have other issues that just money. DAL knows that. That is why they have started to put limits on them. Three hrs in an RJ is just too long. This management team knows it.
Also yes, an RJ could make more money if they could actually charge more given the fact that we offer fewer seats, but they don't.
We compete with other airlines, and if they do not do exactly what we do, there is no way to employ that strategy. DAL is stuck pricing tickets with the market.
Fact is that with that market they will actually have a better yeild on the lower priced tickets with a larger jet. The RJ's are very costly per seat mile, where as the larger jets are not.
I will grant you that there are a few markets that will see a bump in RJ service due to the netting effect that we will employ with our many hubs. It will not be as great as you think. Moreover, the merger will in effect keep the RJ's that were there, where there was an actual business case to bring in a large jet. For example places like PIA.
When the 100 seat jet actually arrives in a platform that DAL is willing to sign on to, yes, you will see DAL take 40 or seats off a flight in favor of that.
One thing DAL will never admit publically and almost never personally, is that they have seen travelers actually book away from RJ's even if the price is more. That right there is proof in the pudding.
Also the 76 seat jet is not necessrarly a money maker. What it does, is allowes DAL to offer a "preimum" product to medium markets. That is the sole purpose behind it. Not to make more money.