I do think Aman ran a beautiful race tactically, much better than Symmonds' race. I'm not sure whether it would have made a difference, but Symmonds was nowhere near as smooth as Aman through the middle of the race.
1) Look at their positions at the 200m mark. Aman had to run just a little bit faster than Symmonds, but he was in dramatically better position: Symmonds was blocked by a wall of guys that was not going to be easy to pass.
2) Because of that opening 200, Symmonds had to surge TWICE between 300 and 400 to get up with the leaders. Whatever energy he saved by going out a little slower in that first 200 was now gone, and then some. This section had to be smoother: either he had to get out quicker, or he had to be more patient, trusting his ability to squeeze through as he has so often in the past.
3) Aman wanted to be right on the lead, but as relaxed and smooth as possible. He also had to protect himself from getting too boxed. Twice people came up on his outside shoulder, and both times he challenged, but subtly. When Symmonds did it, he challenged but ultimately let him past. That way, Aman was still running relaxed, but Symmonds had to surge. The next time, Aman was in real danger of getting boxed on the backstretch of the second lap. He stayed smooth, but did just enough to protect himself. If he gets boxed there, there's no way he wins.
Ultimately, the key was that Aman expended a lot less energy than Symmonds did between 200 and 700. He was a few meters slower over that stretch than Symmonds (less than the margin of victory), but more importantly, he ran significantly more smoothly.
Between 100 and 200, Symmonds and Aman each had a guy coming up on his outside shoulder. Aman fought his off - probably running slightly faster than he wanted to, but putting him in great position. Symmonds let his go. He almost looked like he slowed a little to let him go. But letting that one guy go was equivalent to letting 4 guys go. It would have been just a little bit more energy for a lot better position, tucked on the rail right behind Solomon.