Pre i6 (I think) the aggro limit was limitless. However, although not all were bothered by this, there were some players who felt this was causing serious issues due to Fire Tanks herding entire maps, pulling every NPC on that map to a small corner, and Burning the NPC's down. This was extreme. The Developers heard the cries of the vocal, and implemented a change that was equally extreme, just in the reverse of the original extreme.
The game went from one ridiculous to another ridiculous. On one end, whole maps were being herded and farmed (not much different than how players now farm AE missions today) to an extreme end, and now on the other hand, with the new aggro limitations in place, we get one group of NPCs fighting us, while the other group who stands right next to us, just stand there...oblivious to the fact that we are beating down their buddies.
Before the change was made, the NPC's had a certain realistic feel to them, because if they were within range of you, they were going to attack you, regardless of how many NPC's you have on you. The game had a bit more risk involved, you had to be smart to move out of the way of patrols, or not let the fight get too far away from a controlled location.
Now, you have NPCs literally standing 2 feet away from you, doing nothing, while you are smashing the socks off of their buddies and rumbling the building with a hail of powers.
My suggestion is that we increase the limit on aggro. We don't increase the limit to a point that we get back to the original extreme, but we increase the limit from 17 enemies, to 30. This allows a group to have the attention of 2 mobs (in case mob two gets aggroed) and a pathing mob. This also brings back that realism the game once had but has lost, without turning it to the ridiculous herding craze it once was.