No, it only fails because it doesn't do WHAT YOU WANT IT TO DO. There's a difference, and you should understand that right now.
First off, 5 GHz is useless indoors. 2.4 GHz will get you further, as it's meant for indoors. Lately we've found out that 5 GHz is BEST outdoors, and can really hit a good range.
Now, you obviously don't know what QOS is, because it has ABSOLUTELY NOTHING TO DO WITH RANGE. It stands for Quality of Service, and applies to bandwidth management for clients. Certain packets take priority.
You probably meant to say Quality Control. There's a difference.
You really should do your homework before buying something. You obviously want a router that does concurrent 2.4 GHz and 5 GHz. If that's the case, then look at the DIR-825.
As far as your wireless signal goes, just because you put it on a higher band, that doesn't mean that it's better in one environment. You also need to understand that antenna placement helps a lot too. If you are trying to use "N", it requires all three antennas. Placement is KEY. And again, 5 GHz = outside, 2.4 GHz = inside.
Spend some time around here reading some of the tips and tricks we've mentioned in a lot of the posts. It's mainly repeating stuff, but it's all the same, and they DO work.