Here's the scenario: My army will contain a 2nd Gen. Slann, a JSOD & a Lvl. 1 Skink Priest. If I'm trying to make an all around list, don't I have to give the JSOD a magic weapon instead of the GW b/c of ethereals? Wouldn't relying on magic and SCR leave me vulnerable?
Well it depends. Generally speaking, you should be fine. Spirit Hosts and the occasional banshee/wraith unit wont mess with you too much, and a 2nd Generation is the most reliable way to deal with ethereals. Most competitive armies rely upon weak magic (1-2 lvl 2s), and SCR. The great thing about a Slann, is that when you see a great deal of ethereals across the board from you, you can take the default spells from Fire, Death, and Light (especially light), and have 3 cheap spells to throw out (2d6 +1 on a 5+ spell well ensure several get through before you cast larger spells). As far as the JSOD goes, you have to way the liklihood of opponents when you try to create an all-comers list. Besides vampire counts, most ethereal characters/units are caused by magic items/spells so will not be seen very often. On the otherhand, you will see chariots much more often as they make an appearance in some form or another in almost every army (Emp, Skaven, DE, HE, VC, TK, OK, O&G, HoC, DoC, BoC). Although you surely also have kroxigors, the JSOD provides a great deterrant as his 18" charge w/360 will restrict chariots from entire portions of the battlefield. Also, the low points cost of a JSOD compared with a Kroxigor unit makes it more reasonable to have him chasing 1-2 chariots, while Krox focus on being can-openers. Not only that, but the magic weapon will cost more than a GW, and generally speaking will not give your JSOD a significant improvement against anything beyond ethereals.