I realize this is a bit of a necro but I figured I'd chime in in case other people see this later.

There are three broad approaches to powerleveling in EQ1. I really don't know what is the fastest. Advice will point you to what is basically option 1 generally, because of various gimmicks, techniques, and such you can garner massive amounts of exp. The third is also really fast, and in general terms, is probably practically faster than trying to optimally exploit option 1 (since you will spend a lot of time searching, experimenting, and failing before you get it right.) 2 and 3 can be done by anyone.

1. The most popular option is to group them with a high-level character and proceed to slaughter en-mass. This seems to be what swarming is alluding to. This is probably the easiest; but there are limitations regarding getting EXP with the PLer.
2. Another option is to simply buff (DS's are great) / support (heal) out of group a low level character. E.g. pocket cleric or pocket druid. This can even be done in concert with grouping pretty easily; as long as you stay out of instances.
3. The fastest option by far is to use a tank class with an AOE taunt in concert with a damage shield to convince a large number of monsters to stay mad at you, and continue to hit you, while dieing from passive damage. The PL'ee then tags them.

The third option can be tricky, and it's always possible they will patch it at some point but its unlikely since it's been available since launch. It works better when done from on high to relatively low levels; after that option two would take over. A simple example is a SK (self DS+ AE Taunt) with a druid (casting their DSes and heals on the SK.) Then a Wiz can cast their low level PBAOE spell and do 5 damage to all the monsters. When they finally die, the DS has done 99% of the damage, the SK has done 0%, and the wiz has done 1%; so the wiz gets full exp. E.g. the SK/druid might be grouped, but the wiz is not. (or at least, only grouped with characters his level). As a bonus, this works on monsters that summon, since you are never out of melee.

In a bit of reminiscing, this can get quite elaborate with mercs; once I had my SK, monk and bard grouped (with healer mercs) with my shaman, cleric and mage in a second group (also with healer mercs in case they pulled agro), all to powerlevel a druid. This allowed me to continue to do this well after I could have switched to just letting the druid slum with the SK. As I recall this character was level 68 or so with capped AA's, and at the time the SK was only level 75 or so. (long time ago, relatively speaking.)

In the past I generally preferred option three until the new characters were high enough to contribute to grouping with the main team; and then just drag them around with the group until they were basically indistinguishable from the rest. Option three is blazing fast; your skills tend to fall far behind. That same druid could barely cast spells (beyond their lowest level PBAOE anyway).

the main caveat is that it's been a long time since I actively played; things could have changed, I doubt it though.