DL hasn't announced new schedules in response to AA's recent announcements. But AA/US have a larger presence in ATL with these announcements than DL has from other AA hubs.
I can absolutely assure you that Dl will find no shortage of AA markets in which it can grow.
and, no, AA's schedule from LAX to ATL is not anywhere near competitive. A mid-morning first flight, a late afternoon, and a departure after midnight are not competitive with what either DL or WN offers.
And, I have said for years that DL will focus on MIA, including LAX, in time.
And there are more and more reports that DL is working on its own gate acquisition plan at LAX that validates what I have been saying all along - that DL is not pushed into a corner as some would like to think.
DL has not announced its spring and summer 2015 domestic growth plans. It will be clear when that happens that DL is serious about growing its network and protecting its key markets just as much as AA is interested in pushing into DL's key markets - and then some.