From another pax perspective, I feel that they need to get the customer service to improve for both airlines. I have always have had a love/hate relationship with BA because when they are good, They are very good. Unfortunately on the flip side, I have had many poor trips, some even on Business Class. Unfortunately you tend to remember the negatives more than the positives. Unfortunately Iberia long-haul are the pits. After 1 hour of a flight, the cabin crew are absent until landing. Food is a hit or a miss, not just on quality, but whether you get any at all!, even on 12 hour flights.
I am also a regional pax, and I am amazed anyone routes MAN/LHR/MAD/Any S.A. Destination. It appears madness. 4 flights when 2 will do. I will fly LPL/MAD on EZY and IB from there, (although I am looking at alternatives to IB). This routing, despite booking in luggage again, is a lot less hassle and I can chill out in the lounge if connection time permits. Another positive is that you avoid the long haul tax this way. However, I put MAD in the same category as LHR in trying to avoid. Both have good elements but can be a nightmare at times. The new terminal at MAD is the only one I know where you have to catch a train from one part of the terminal to another. Its caught many pax out, including myself.
I'm hoping that the merger will bring about the best bits of both airlines, and I certainly hope that that everyone employed will keep their jobs, particularly in these uncertain times. I might even be tempted to use BA again on some flights, rather than the odd associated flight in the last few years such as GLA-Stornoway and CPT-Port Elizabeth, hardly mainstream.
I disagree with you, as a frequent flyer with Iberia, they do offer a reasonable meal service on long haul flights. On european flights, you have to pay for it.
I agree with your opinion about the cabin crew, as they are well known as not been very serviceable and been also unfriendly.
Concerning the train service in Madrid from T4 to T4S, I´ve seen that kind of trains on many airports around the world and it doesn´t suppose a problem for nobody, except you.