Exactly. You have no idea what kind of training he was doing to run that 3:28. He was training for speed, he was not training for 5k/10k shape. Just admit you are wrong. Seriously, if 5k/10k training takes 4-5 seconds off of a 1500m time, but doesn't improve half marathon time, then it's obviously not really 5k/10k training. Especially if the time period is around a world championship. Those races are almost always about kicks not endurance. Again, just admit that you are wrong.
No, you are being dishonest about Farah's improvements. He chopped off lots of time from his 10000m time in 2009-2010 without Salazar. He ran his 27:28 all alone. The gap to second was something like 50 seconds. Obviously he was good for much faster. He isn't the type who can run without rabbits.
Sure, he ran 12:57 fading. Doesn't necessarily mean he was that much slower than 12:53 with a 54. The fact alone that he was fading means he could have run faster with better pacing. That's what fading means. Exactly what were the splits in that 12:57 race? One of them was obviously fast or at least too fast for Farah at the time.