We just recently recruited a player that was reluctant to join another 25 man guild because since the start of Throne of Thunder the 3 he's been in have either dropped to 10man or disbanded. The guild he was in for 2 years dropped to 10man because they were stuck on horridon hc for 2 weeks while other 10man guilds were facerolling ji-kun and getting ahead on progress.
The second guild he joined disbanded as he got there due to players not turning up.
The third guild had 12 people leave to form a 10man guild because they were tired of people making the same mistakes , its pretty clear that 25 hc content is very unforgiving this tier where you can't have any weak links, in the past you could carry 2-3 people in a 25 man guild but this tier has been so finely tuned that you just can't carry anyone if you want to get somewhere this tier. I think 25 man guilds that have a roster of 30 good players will be fine but I think there is more pain to come for the 25 man raiding scene this tier.