There's far too much wrong here.
I'll start from the top.
The point of gear scaling is so you don't overgear the dungeon. Using SoO gear, in fact, is worse for challenge modes than using ToT gear (and PvP gear is also close, however Grevious is better than Prideful). This was the case on retail, albeit it's possible it was due to bugs there. Nonetheless, SoO gear or Prideful or Grevious gear makes literally no difference in challenge modes. Tier sets are not supposed to work in the dungeons, and while trinkets do, their proc rate is meant to be scaled down as well. You can see the gearing rules
here or
here.
Moving on, if the Rated BG achievements worked, I would already have the 40 win rated bg achievement and mount. I have 62 wins, and trust me, I am not the highest here. I'm sure you will find many players with 100 Rated BG wins. If you want to do rated BGs and work hard on making teams, I'm sure many guilds will play you, Hysteria being the most hungry for Rated BGs currently.
Maybe you don't understand English that well, so perhaps I am to blame for not being clear. I'll try to break it down a bit easier.
1. Currently Challenge Mode is bugged and is a joke. As stated above people can solo a dungeon and get silver.
2. Because of 1, I am saying currently Challenge Mode rewards are a joke and not valuable, because every noob has them, such as yourself.
3. If 1 did not happen, aka Challenge Modes worked properly, the rewards would be valuable because not everyone will get them
4. This is why I suggested removing all rewards and re-opening CM when they work
To recap, MY argument is not everyone can have it if it works. YOUR argument is that everyone can have it.
Based on YOUR argument, if everyone can get it again, then we have no problems with deleting the rewards and making people earn it properly.