That's like saying having a realm first achievement for killing heroic bosses was a bad idea because it encouraged people to use exploits, see Lich King saranite bombs or Garrosh solo healing. That's not required for realm first, it was something the world first group did.
95% of the people in the race didn't need or use exploits, I've had realm first warlock in cata and realm first 90 in MOP, all I did was quest.
I didn't even miss any sleep it was such a quick sprint, let alone need to exploit.
And guess what? I'll be doing the same race again, regardless of a FOS, because it has nothing to do with a FOS and everything to do with player mentality towards wanting to get to max level asap and start prepping / enjoying max level content, hell - I imagine most of the server will still know who hits 100 first regardless of being spammed with an achieve.
People complaining about these things really seem to have no idea what getting realm first entails and are blinded by what news sites have reported world first taking, which is a different race entirely, and neither they or blizz devs seem to realise that removing a FOS changes nothing, the achievement is still there, it's just a real achievment, not what the video game gives you a little badge for.