Wisdom is really pretty weak for clerics once you're in BG2, see:
https://baldursgate.fandom.com/wiki/Wisdom
Viconia gets 2 level 1/2 spells and 1 level 3/4 spell. A level 15 cleric has 6/6/6/6 of those levels as a baseline, you probably don't care about more low-level spell slots. So I wouldn't worry about Anomen's slots vs. Viconia, they are both effectively just as good clerics.
Aerie's problem is that multiclasses don't get mage HLAs and level 9 spells until 6M XP instead of 3M XP, which is mid to late ToB compared to mid to late BG2. And unlike pure clerics she actually does fall significantly behind Anomen or Viconia in cleric spell progression. Characters like Imoen or Nalia on the other hand are basically ideal, they get most of what you wanted out of thief levels but still puts all their useful XP into mage and get mage HLAs at 3M XP. Still not as great as Edwin, but you have to have a thief in your party. For the record Edwin will cap out at 8 level 9 mage spell slots while Aerie has 3.
Disagree that Keldorn is the strongest fighter since the ideal weapon setup is dual wielding for more attacks and having grandmastery in your chosen weapon. Anomen and Korgan take that crown (I guess you can throw in all pure fighters but the others have bad proficiencies). Obviously dispelling is great, though it's not TOO essential in a non-SCS game.