Looks simple to me.
That is still more compliceted than this:
If they really need the A319 for a certain number of missions it won't make the fleet harder to manage since the pilot pool will be the same with the A321. To me simplifying the fleet means having the fewest number of pilot pools possible to reduce the amount of differing training required to provide, Different engines are a non issue today because of power by the hour deals and maintenance of all the members of one family will be extremely similar if not identical --> the fewest number of aircraft families makes sense, even if sub families will go up.
The A319 is here to stay. They have been useful for AA and removing them from the fleet creates a sizable gap.
Here's the problem with this lineup, and I agree it's very simple, but consider that AA has not taken the A350, and with the latest news, there's a chance they may never. It may not be worth the cost of acquisition and integration for a new type, especially a type that arguably had its role already filled.
Operating the 777 and 787 is not a bad move. If they want growth, the 787-10 and 777-9 can be added with ease, and additional 787s will make fine 77E replacements.
If AA decides to keep the A350, a scenario like yours probably makes perfect sense. Only If.
Two subfleets each, both efficient, all types have a role. I'm guessing it all comes down to cost. If AA can be mostly 787 with the 777s working high denisity and premium, I have no doubt that's what AA will do.
I have no doubt the A319 has been useful, or they would have meen axed long ago, but could they not be replaced with 738max with the performance boost option? That's if the performance from runway is the reason they are useful, I'm not sure if it is.
I know the 77W replacement is more than a decade away, but that must play into this as well as those planes can be replaced by the 779 or the A35K, and that will be linked to the 77E replacement. Going 787/777 route will leave the 779 as a small sub fleet later (after 77Ws are gone), and I feel that may not be as efficient/profitable as going 787/A350 route with an option to expand on the medium range flights to the 78J as it is slightly more efficient at those ranges than the A359. Also gives the most amount of flexibility along with efficiency, hence my opinion on which way the A350 decision should go. 78J and A359 for the short and long routes that need the capacity, A35K for premium routes that can support even more capacity and the 788/9 for routes that can be operated more profitably with less capacity/less premium cabin. Each model would have a specific role and most would be interchangable to to all other routes if circumstances required that.
Going the 787/77 route would axe (make less profitable) the medium-large long routes where the A359 would be in the other scenario and still wouldn't save on pilot traning as 787 and 777 pilot rating is similar, but not the same.
We can agree to disagree on which would work best in our opinions. I have my preference for the A350 and you have yours for the 779, nither will be a bad choice however.
As a side note, just had my 1st experience of the A350 and it was superb! Quiet, comfortable and spacious. My best experience by far out of any plane I've flown thus far. Note I'm only commenting on the plane and not the service proivided since that is so different with every carrier.