The A330-900 would be a better fit for the direction of AA's network than more 787s. While the 787s would be a commonality advantage, all but a handful of AA's routes don't need the range of the 787-8 or -9 or the capacity of the 787-10, which is unlikely to change with AA's strongest hubs of DFW, CLT, and MIA being where they are. The A339 by contrast is well-suited to servicing medium haul Europe and Latin flying as operators like DL and TAP have demonstrated, and likely available on a more accelerated timeline than the 787s.
Throw in a handful of 787-10s to replace the -300ER flying to places like LHR (do they even fly that plane on any routes that actually need the 777-300ER's full range capabilities besides SYD?).
The A339NEO is a big plane too. Yes, not as big as the B787-10 however AA can use the B787-10 for many routes and literally replace its B77E's on a 1-for-1 basis.
My guess is that its going all Boeing but we'll see.
The 787-10 is almost an exact replacement for the 777-200ER (in terms of size and range) while maintaining type commonality with their existing 787-9 fleet and delivering unparalleled fuel efficiency per seat on their shorter/denser LATAM and European routes. It's basically guaranteed.
If they do get an A330neo, it would be to replace some of their older 787-8's, but I don't think those are up for replacement. And I don't think they have any plans to grow the size of their widebody fleet in the near future.
The A350 is too big and expensive for them and they don't fly (or plan to fly) any routes that would require the extreme size, range, and fuel efficiency. It could potentially replace their 777-300ERs one day, but not any time soon.
I find it (moderately) interesting that in my adult lifetime we've gone from the excitement of the A380 to "the A350 is too large to make sense for a global long-haul carrier".
Out of curiosity I looked up Vasu Raja to see what he's been doing since leaving American. According to his LinkedIn he started a company called Dihedral, which is some sort of data company to "help companies move from disconnected data to active "customer orchestration." They strive to "make happier and more valuable customers" which is amusing given the job he did at American. After reading the word salad of a description I don't really have any idea what exactly it is that Dihedral, and Raja, do, but there you go.
You do write that AA needs to replace their “aging 777-300ERs” but those planes were delivered 2013-2016 and have plenty of life left in them. It’s the 777-200ERs that will need replacing in the next decade(ish). So very glad they are getting an interior refit in the meantime and at 23-26 years old plenty of life left in them too if properly maintained.