Most Over/Underrated Class?

[diplomancer]

Yes: the ranged weaponry on skeletons and the intelligence of the Necromancer. If you look back on this thread you've probably seen repeated mentions of the need to avoid Fireball Formation, which is also Destroy Undead formation. As long as you use intelligent formations, an AoE is only going to destroy one cluster of them, which could be e.g. 6 skeletons = one 5th level spell slot. And presumably you did some damage in return while the cleric was getting into position (since Destroy Undead is range 0), so you got value out of that level 5 spell slot.

Basically, Necromancers are mentally prepared to treat skeletons as expendable and play accordingly.

Well, if you are 9th level (at least) fighting the equivalent of 6th level clerics you will most likely prevail.

But if you are 9th level and fighting the equivalent of a 6th level cleric, he is probably a somewhat minor minion of your opponent, who nullified your best spell slot. Doesn't look like a promising beginning of a fight to me.

Also, 30 foot radius is BIG for anything that is not an open field. If your skeletons are in the same room as the cleric, they will probably all be affected if the Cleric is smart enough to position himself before using TU. If they are not in the same room, they cannot probably attack very well, and, once you bring the "second batch" in, the 6th level cleric has another channel divinity ready.

It's a good gimmick for open field fights, but very high risk strategy for an appropriate level dungeon.

Simpler way to put it: Trading off one 5th-level slot for one action and one use channel divinity looks like a bad trade-off.