Just a few points here.
The fares charged for the various seat types are determined by what the market will bear. Fares charged have no direct relationship to cost, although the accountants behind the scenes are making the comparison of course. If you just stick another 5" room on some seats and find you can sell them for 10 times as much, so be it.
In an industry where it is by no means unknown for every passenger on the aircraft to have paid a different fare, regardless of all the seats being simlistically the same, it is apparent that charging is based on what pax might pay for any combination of circumstances.
Seem to recall American's lowest prices when they increased the pitch were typically nearly double that of competitors.
There seem to be a lot of urban legends about American's scheme of about 15-20 years ago, MRTC (More Room Throughout Coach). I was actually a user of AA at the time and experienced it. The fares were not
significantly different, as otherwise I would not have been using them. And contrary to what I have often read, many of the pax on board actually did notice it, and commented on it, and seemed to have based their airline choice upon it. What happened was there was subsequently a major change in how US airlines handled their regular passengers, who now seem to get, and even expect, upgrades to the cabin above for their "status", which has among other things resulted in a collapse of paid-for First Class revenue on US carriers, with economy seating sometimes only at 80% occupancy while the F cabin in front is stuffed full of upgrades. Nobody seems to pay for F in the US nowadays, whereas everyone seems to expect it. Most bizarre !