What is HOS? Was guessing Howling Stones, but not positive.I recently did my beastlord 85-110, I had a full group of 110's but you could do this with your bst and pal+ cleric mercs.
I went to the static zone of GMM and killed stuff until my beastlord was 95, then I did the gmm instance until he was 110 (kill everything don't loot chest and do it again)
Otherwise sathirs tomb, same thing is probably faster or you have a paladin it might be faster to do HOS. In HOS you could maybe drop the mercs (dps mercs don't do enough dps to warrant their spot in a group. A 110 paladin can tank and do the group healing in HOS (or FM for that matter) I would just invite randoms that are lfg instead of using a dps merc, if your beastlord is doing well, I think a dps merc is probably taking more exp than he's adding to your group in damage.
RoS isn't FTP but not "current" so that's probably why it has less traffic. I'd be interested in more grinding spots there as I'm bored of EoK (and it gets crowded).I found that if you go to Overthere in the RoS expansion then head to down into the valley where all the roaming scorpions are and set up camp near the middle Rigelon the Watcher spawn (there are three... do the one in the center). From there just pull scorpions at your own pace. The exp is pretty good, multi pulls are a breeze... almost zero traffic as I never had a someone come past me.
I would avoid setting up camps inside the little chambers as MQ2NAv sometimes gets hung up on a corner.
Drops are nice for vendor selling and /barter as well as the spell vendor not far away.
I've done the lower valley as well but I park next to the ghost peeps. From there you can pull them and the southern camp. Swarm pulling rats is decent exp as well. GMM is great for 95 plus. If you can handle the static zone go earlier.I took a different route. I brought my 90's to Valley of Lunanyn and swarm pulled the southern camp and the cave (Reega's) while moderately AFK'ed. I would also pull the oustide of the cave system. I'd alternatively use Arthicrex in Underfood it camped. Same thign i'd mass pull and AFK netflix. Took like an hour each level 90-95. But more my play style. At 95 moved to GMM instance.