But you are not saying in which situation.
Pretty much all of them. The Starseer has a chance to give a CP on a 4+, has the ability to grant anything that SHOULD wish to charge the ability to roll 3d6 and an innate spell that gives either +1 save or -1 save which can be huge. It's a rock solid Warscroll, especially for the points. Granted I'm coming from the perspective of Orruk Warclans where...well look at the Weirdknob Shaman :/ I actively love the Wurrgog Prophet and I feel like the Starseer is a better wizard. Easier to get +1 to cast, and can even get access to a horde clearing spell just like the one on Wurrgog Prophet's Warscroll. Pound for pound I'd say the Starseer rocks.
The Starpriests ability to add mortal wounds on wound rolls of unmodified 6's is worth its weight in gold. Literally anything you put it on becomes automatically better, and more often than not it's used on something that's spammed anyway, like 40 skinks, 20 chameleon skinks, or high volume attacks like 6 Kroxigors which is at worst 30 (24 drakebite maul, 6 bite) attacks. Not to mention it too can give a CP on a 5+, and has a nice defensive buff -1 to hit. Put that on Daemonettes or the like and they're suddenly 5's and 4's. Not to mention any Slann can channel spells through him.
I can't see a situation where they're bad unless you're taking like MSU low attack spam ? Like improving the save on any one unit is amazing, so good, in fact, they changed Mystic Shield to just be re-roll save rolls of 1... Plus it can debuff your enemies! The charge ability is typically a spell, or a roll on like a 4+ or something for other armies, and they both can give CP! Like I'd bring them for that alone. I'd bring the Starpriest JUST for the mortal wounds nvm he's a wizard.
I think they're fantastic wizards. Slann and Kroak are just so powerful it makes them look bad in comparison, but with all the interlocking synergies they fit right in and can easily get +2 to cast as well.