Re-using this thread for an additional update.
In the upcoming patch 5.4.7, we will be making a few small adjustments to the 10-player Heroic Garrosh encounter. There a few factors that contribute to a disparity between the difficulty of the encounter in 10-player mode versus 25-player mode, and these changes are intended to help correct for those differences.
We are slightly reducing Garrosh's health in all phases (by roughly 5%).
The fight as a whole is a series of hard DPS checks, where failing to meet certain benchmarks makes things tremendously harder if not impossible, but extra DPS above and beyond that threshold doesn't necessarily help all that much. We're seeing some kills (a minority, but some groups nonetheless) feeling the need to single-heal the fight even at this point, and that has a number of negative gameplay and social issues. We can't really prevent single-healing (other than by increasing the outgoing damage, which isn't an option at this point), but this change should at least make it so that no one feels they need to single-heal in order to meet the various checks, without lessening the coordination requirements of the rest of the fight.
We are reducing the health of Minions of Y'Shaarj (by roughly 10%).
Most 25-player groups are able to kite and otherwise control the Minions thanks to the additional available manpower, while 10-player groups generally have to kill them. This change should improve parity between modes by reducing the difficulty of this particular mechanic for 10-player groups.
We are increasing the clump size required to trigger an Iron Star in the final Heroic-only phase of the fight from 3 to 4.
Iron Star detection previously required 3 players on 10, and 8 on 25 (a standard ratio), but this causes a discrepancy when it comes to the overlap between Bombardment and Malice. Malice requires 2 soakers on 10H and 5 on 25H (again, a standard ratio), but this means that the total clump sizes required to handle Malice are actually 3 and 6 respectively, such that a 25-player group could cover soaking Malice #4 (which fully overlaps with Bombardment) without triggering Iron Stars, whereas a 10-player group generally could not. This change should, like the rest, increase parity when it comes to this mechanic.
"Why did you wait this long to make these changes?"
We're very conservative when it comes to reducing the difficulty of a Heroic final boss, since the entire point of such encounters is to represent the pinnacle of raiding challenge. For most of the initial months of the patch, the sample size of players killing Garrosh on each difficulty was too small to draw meaningful conclusions about the relative difficulty on 10 vs. 25, but now we've reached a point where it's clear that there's a problem, so we're taking the above actions.
"Thanks Blizz, way to nerf the only hard fight left in the game..."
Sorry, we do wish we'd gotten the tuning right in the first place. 10-Heroic Garrosh will still be plenty hard -- this is just bringing the encounter in line with its 25-player counterpart.