Problem is valve insists upon being stupid with achievements. Just separate the achievements and new weapons. The new weapons are why I really don't play TF2 anymore. I don't feel like grinding to get better guns (a number of them actually are strictly better.)
As for "cheating", bullshit. They are still playing by the game rules. Its no more cheating than someone who bought a character on WoW. They were just smart and skipped the grind they didn't enjoy. If you enjoy the grind, great. If you hate the grind, why have you been kissing Valve's ass, tell them they did something stupid. In the end they have no advantage over you.
The number of achievement farm servers and the achievement hack is pretty solid evidence valve screwed up the achievement weapon link. I can only hope companies start to wake up and this plague of companies adding levels/grind in wholly inappropriate places ends. Keep it to the single player games and the shitty MMOs.