first, DL cuts back on a seasonal basis across its entire network. none of the cuts are anything different from what DL does on a macrolevel outside of the peak season.
as to fuel prices have been good for all airlines but it is not the justification for DL's SEA hub and low fuel prices don't make or break the hub. SEA was designed to replace CONNECTING capacity that flows over NRT while leaving DL's Tokyo operation focused on the local market. SEA was chosen because it is the closest city in the continental US to Asia which makes it possible for DL to start routes with smaller and less costly 767s and 330s and because there is a better opportunity to connect every market in the continental US and Canada to Asia via SEA than for every other hub. AA has indeed built up Asia but DFW will never serve as a viable primary connecting hub to/from Asia solely because of its geography.
Low fuel prices have given AA breathing room to grow its Asia network, for DL to grow its SEA hub, and for AS to defend its SEA hub. None is any less than the other.
As to the article, there are several factual inaccuracies. Data shows that over the past 3 years, DL has added almsot identical amounts of longhaul int'l and shorthaul US capacity from SEA. Thus, DL's RASM movement is not any more biased because of building up domestic vs. Asia flights. on a seat basis, yes, DL's domestic growth has been much larger but RASM is calculated on ASMs. The statement that DL's statements regarding RASM are wrong
because DL is adding more domestic capacity based on ASMs is simply not accurate.
It is also not accurate that RASM is not known for DL at SEA. DL has never reported RASM by city and SEA is no different from any other city. It can be calculated using DOT data eventually but there is only about a six month lag on that data for any market - growth or not.
The article assumes that someone has to lose in order for DL to grow and that simply is not the case. DL serves a different set of markets, has been very careful to add growth which it can support on a long-term basis, and AS has grown in markets that overfly other hubs and also have lower amounts of connecting demand beyond SEA.... thus, the notion that either carrier's strategy is incompatible with the success of the other is flawed. And based on enough information that is known, DL intends to start operating a pad operation at SEA in 2016 indicating that they are confident that growth will come. DL doesn't need to match AS one for one in terms of total capacity or the number of markets served. Likewise, AS will never fly longhaul int'l and won't get the benefit that DL has even with AS' partnerships including that AS cannot negotiate pricing involving its int'l partners' int'l flights - so both carriers have strengths and weaknesses in terms of their total offering.
Finally, DL is growing in both SEA and LAX and also still has SLC, something that only UA can come close to duplicating in terms of network - and UA has been badly stumbling in so many ways that DL's growth is likely coming at UA's expense far more than AS'.
It is hard to see how SEA will play out but when so many people including here have flawed data that they use to make flawed conclusions, it is highly unlikely that they will come up with an accurate long-term undersstanding of what will happen in the SEA or Asia market.