Who cares about the ATL metro area? That has little or no impact on whether DL flies to/fr anyother place from ATL? It does have to do with connctions and Delta was doing quite well with them when they did fly the route (that entire summer the flight was above 97% capacity and that was on a MD-11). For that matter if you want to talk about O/D Coke's headquarters for the Middle East and Asia is Istanbul, and they move a lot of people on the route, which is always a good start.
Yes TK is a much better carrier today then before, I am in fact in addition to being a Dm/2MM on Delta a multi year E+ on TK. What you say about the catering in Biz is not true, the DL catering and drink selection is still far superior, in Coach however TK is far superior. Seatingwise it is not so simple. The new TK flat seats are pretty good, but at the moment you have a 50/50 chance of getting them to NY, when we see what sort of a/c the third flight is,then we will know if the chances improve. Furthermore since the last season DL is flying its latest flat bed product on the route, so there is no longer that particular advantage. Regarding IST-LHR, you are welcome to look at my posts on the subject on the BA board over the last 2-3 years. If you get a widebofy l/h a/c on the route it is exponentially better than BA, however if you get an A320/321 on the route, it is no better or worse, although the catering is a bit better. The problem is that currently on most days you are looking currently at 1 out of 4 flights as a widebody currently and 2/5 on Saturday. OTOH the last few months if you took the BA 767 flight you would get the l/h 767 rather than the short haul.
Yes the TK lounge is probably in the top three worldwide currently.
Vuelos, what on Earth are you talking about? DL has never run the flight 2x??!! Quite frankly, sometimes I fly to JFK O/D, otheer times I connect to somewhere else, the times that I connect I would prefer to do so in ATL if that were an option and have found myself connecting at CDG or AMS with KL or (shudder AF) in order to avoid JFK connections.