A tad hyperbolic a reaction there for the poor Soothsayer.
Mind control is a beast. You gain a soldier, they lose a soldier, net gain of 2 men on the ground for you. Plus cast it at someone just about to escape with loot and the loot is now yours!
Reveal secret is practically a free treasure and turns what would be a 3-3 draw into a 4-3 victory for you.
Combat awareness not only makes your troops hefty fighters but also makes them harder to hit at range.
Not at all. Whilst Soothsayer has some ok spells, there is very little reason to take it as a Primary school as it offers so little and its aligned schools are equally weak as a set.
Mind Control is just as good when taken in an aligned school - since you're happy casting it at higher numbers (harder to resist). It is Soothsayer's best spell, and probably one of the more powerful spells in the game, yet ironically it doesn't make a huge difference casting it from a non-Soothsayer Wizard.
Reveal Secret is a decent spell but is kind of hard to cast without XP (even if you do get 2 chances at it, it's still far from a sure thing) and all treasure takes one of your guys out of the fight - there are only so many guys you can afford to lose - so it is far from free.
Combat Awareness is absolutely horrible. It casts on a 12 and requires touch range, and whilst more fight is always good, +2 fight is not a massive buff given the opportunity cost of casting it over another spell. Even Strength in the enchanter school, 2 easier to cast and castable at range, is often a hard decision as to whether to cast.
Awareness is an ok spell - just OK - it doesn't come into play very often and even then, initiative in Frostgrave is (somewhat counter intuitively) not always a big deal. At least it casts on an 8.
Every other spell that Soothsayers have is awful.
Wizard Eye is very range limited and requires LoS to where you place it plus only has a 180 degree FoV, making it very poor in practice. It won't let you see to the other side of a wall because you need LoS to the facing on the other side of the wall to cast it in the first place. Furthermore, since it does need LoS to somewhere where you may place it, you have to expose yourself to the enemy and spend an action casting it before you do anything offensive or defensive. It's a really bad spell.
Willpower has a decent effect, but either you'll be casting it after the fact when someone is already under the effects of a resistable spell or pre-casting it which means your opponent will simply choose another target. In practice there are almost always decent spell targets so that isn't a big deal. Add to that that many opponents won't even use resistable spells as there are other options and you have another narrow use spell.
Reveal Invisible is a decent spell with another very narrow use. Could easily be taken as a secondary spell from any other school's caster.
Forget Spell casts on a high number of 12 and can only target enemy casters who always have decent willpower (and will improve it with XP). Furthermore, as the opponent learns more spells, it becomes weaker and weaker. Plus you have to get LoS to their casters to use it. All round weak.
I wish Soothsayer was better as a primary, but unfortunately it isn't. It suffers from too many niche spells, casting numbers that are too high for the spells, and some outright poor spells. If Combat Awareness was the same as Strength for Enchanter, and if Wizard Eye was not useless (eg if Wizard and Apprentice could see through eachothers Wizard Eye, and/or it didn't need LoS to its casting point) Soothsayer would be fine.