There's a few zones where spawn density is high enough that doing Slayers is actually worthwhile - and its a fun change of pace from doing quests. It promotes casual group play - or at least using the Social panel to find active runs, at least. Its a great option for new players who might not be able to handle high-level quests on higher difficulties.

But for most of the zones the spawn density is abysmal and trying to get to your next milestone is like pumping molasses. Clearly its not an issue in general if we can have zones like Orchard or Thunderholme or parts of Barovia where mob density is worthwhile - though yes, Orchard was a lag issue for a while.

Lets increase the number of mobs that spawn per spawn node so that we can see more Orchard-style play in other zones. 3BC stands out because its slayer deeds are worth about as much XP as the "big three" Epic slayers, but mobs are so sparse that spending the same amount of time yields way fewer kills. I'd say 3BC needs to be about doubled...other zones like Cogs or GH could use a tuneup too, to a lesser extent. Some like King's Forest need even more.

If it was worthwhile to get to, say, 400 kills in every Epic slayer zone, I think that would be a huge bonus for variety in Epic and allow people to break out of just running Saga chains.