The issue with Jungle Swarms, is that, like Chamo Skinks, they have become a tactical unit. Although Warhammer is won by the amount of combat resolution, the game is normally determined in the movement phase.
While Jungle Swarms are not the massive tarpit that they used to be, a small unit (1-2) can do wonders in a game. There small frontage means that they can normally squeeze through enemy units and redirect charges more easily than other skirmishing units. Although they cannot bait and flee due to them being ItP, they can easily charge units in an awkward position (the flank of a a single ranked light/heavy cavalry, beast herds, skirmishers, the flanks of chariots, etc.) and hold them for one or more turns than a skink unit. This fact means that parking 1-2 jungle swarm bases on a flank or in a terrain piece will cause your opponent to either underestimate and get a unit stuck (and marchblock surrounding units), or overestimate and allow you to grab the initiative with your mobile Lizardmen army. Keep in mind that VC players still took batswarms even when they became undead, and our swarms have poison

.
Chamo skinks, as has been discussed in a previous thread (in fact I believe both of these units have been discussed in previous threads), will not kill much but can ensure that you marchblock the opponents most important units from the beginning. The fact that you can marchblock from turn one
and survive enemy ranged fire (a -2/-3 in the open, and you will normally be in woods or some other form of cover) guarentees that your opponent will have to direct a disproportionate amount of force in order to deal with the chamo skinks.