You have obviously missed that the reasons AA's transcon strategy is raising questions involve:
the 321T strategy reduces costs dramatically over the 762 but it also dramatically reduces total revenues, including about 40% of the coach capacity and a large chunk of the cargo market. If AA was getting the premium revenue already, then cutting the other revenue in order to bring down costs means AA has ensure that the CASM falls faster than the lost of revenue - and that is not a given.
Based on UA's experience with a very similar strategy, the chances are really high that AA will find that they need those coach passengers which they are now saying they don't want.... given that aside from AA and UA's transcon strategies, there is no evidence of a successful niche strategy, it is a real concern.
While AA walked away from a big chunk of the coach and cargo market, other competitors have added capacity in those markets which means that AA gets no additional pricing power as a result of reducing its own capacity. Further, there is new and expanded premium cabin capacity which may make it a lot harder for AA to focus on its premium cabin advantage.
Finally, there is no evidence of a successful niche hub as AA currently has at NYC compared to DL and UA which are much larger and serve markets which AA has so far not only chosen to not enter but some of which new AA has cancelled. Add in that AA is operating the transcons on a niche within a niche strategy (they are carrying only part of the transcon market because they are cutting coach capa city while also not serving many of the same markets that DL and UA serve) an there is every reason to ask if AA's strategy is viable on a long-term basis.
And, there are indeed both similarities and connections between what AA is doing in the transcons and to/from Asia.