Actually, I think I agree with you.

You do not need to be a "big" guild to gain these guild achievements. You need to be an organized guild. There is talk on the forums from people in small guilds that 2-3 people are able to reach the daily cap. As for these achievements, all you need is 4 people to do a 5man and 8 for a 10man dungeon/raid. What does that mean? It means you do not need to be in a big guild.

So who does this change punish? It punishes organized guilds who work together. This change punishes guilds who work as a group and puts guilds who are simply a collection of random players leveling on the same level for doing absolutely nothing as a group.

The problem with your analysis is that many, MANY guilds of any consequence on beta were doing this. Sure there was 5x leveling, but even so, there was a cap. As soon as guilds realized achievements would accelerate guild leveling, it was off to the races - guilds were running everything, and doing everything to hit achievements. The legendary weapons? Reputations? Tabards? Etc., etc.

I simply don't buy Blizz legitimately underestimating and calculating the impact of achievements: Blizz has no legitimate excuse for letting this go live like this and then deciding to change this.

My own guild? We had gotten to level 2. Blizz negligently dropped the ball here.

I completely agree.