This makes sense, and at a "tactical" level definitely seems more logical than the old methods of order lag. So I do think it's an improvement.
I still question the "strategic" decision to doubling the lag on non-prime followers. Lag is one of the worst things about playing muds in general. Games should be interactive. Again speaking generally, I've seen other games where certain powerful skills would have a cool-down time, but the character could still do other things.
Speaking more sloth-specific, it seems silly to look at a Wa/Ma vs. a Wa/Ne. The strongest necro ability is to summon undead. Not only does a secondary necro not get juju but also apparently he'll always have less powerful undead followers than a necro prime (even at avatar levels). In addition to that, all of his followers have twice the lag time. The Wa/Ma on the other hand gets all the blasting capability of a Mage prime except for the extra +20 spelldamage cap.
In short, I think the necro followers for non-necro prime characters have already been weakened quite a bit from the overbalancing feature they once were. Especially if the undeads available have been changed recently to follow the class structure like Supplication was built.
In short, I have two points that I'd like to make:
1) I have always loved Sloth's multiclass levelling system. I mean, the original system where getting a level 36 in your quad class gave you similar skills / spells as a 36 in any of your other classes (triple attack or firewind or whatever). That reflects a certain philosophy where, with enough practice, a person can become skilled in several classes. The prime-only skills and eq were a step away from that original system, and I have learned to accept those. Some recent changes are further steps from the original system. Specifically the reduced capabilities of supplication and summon / animate as your casting class moves down the classo. I wonder if a character with necromancer quad will ever use the summon capabilities of his class if the strongest undead he'll get will be a zombie or whatever. Compare that to a mage quad that still gets firewind (and frostbolt) or a cleric quad that still gets restoration and raise dead.
2) Going back to the lag issue, I'll always argue against inducing lag to players. It's simply frustrating and annoying to be lagged for two rounds. For me, at least, it ruins any fun I normally get while playing. I'm sure that there are other methods to balance followers without adding lag times.