Im still on my first playthrough without any restarts. While it is true that the more fragile classes at the Novice level
(like Mage etc.) have a very thin skin and if focused during one round falter quickly (and every consecutive falter has a bigger chance of kidnap. thats how it is) - this is still unlikely and there are things you can do to prevent that. Usually this is balanced out by the simple fact that you stick them in the back of your formation; not a lot in the starter dungeons can even reach there. (with the aforementioned ratkin only the sorceress can reach rank 4 I believe?) You could train a warrior to quickly get "Guard" (at level 1) and protect your mage. Or at home build a trainee field and train your weakling in Constitution before you send them into a dungeon (so that hey have at least enough HP to withstand one round of damage). If you have +Con equipment that works too (I have a crown of constitution with Con:min 18). Or avoid fights against too many enemies that can reach the back of your formation. The game is fair like that in that it shows you who you will be fighting against. If you dont want to fight them go somewhere else or - if boxed in - retreat from the dungeon.
Buffs on the enemies like Block or Dodge can be dealt with. The Ranger class removes them even with their starting skills. Vulnerability directly counters Block. Id look into that. There are ways to deal. Or if you are desperate just punch through the buff. It only has one or two charges anyway.
Three of my girls got kidnapped quite early. I got them all back by now ( I know Im a loyal dog like that
). I got an Adept team together by the time the difficulty of the rescue missions dropped to Adept, too. The mission can even be easier than anticipated: if you find the room where she is held early and then the exit you can just take her and leave. They are all three cows now. I could change their class but they are wearing one piece that requires lvl 9 in cow before you can take it off. So im doing that. It's really not so bad: it helps them grow their bust. Something I like to see anyway. (up to "Large" at least. I can live with a -5% clearheadedness for my viewing pleasure) And they can hold their own in a fight. Plus at home they can produce milk.
Which brings me to healing. Look into the provisions that you take on a mission at the start more. In absence of milk I recommend bringing bread. These provisions can have two effects - one during battle or one outside battles. You want the outside one. In between battles bread heals your character (make sure to mark them the active one beforehand) by 50%. Milk completely heals the character and doesnt cost provision points on top. Morale healing is tricky: its effect is not additive. You always only heal
to 25% or 50% or 75% etc. (regardless of what the current HP is). So 100% morale heal is most of the time the option you want. But also costly. Use healing at curios at your own risk.
That the one character that a quest tells you to make a prisoner became another class is unfortunate. You can always dismiss the character and the quest - im sure you will soon get another one. Or go through with the leveling up.
I mean look at it like this: you look at your playthrough and see this as
'losing' . But the game is just showing you the different ways your characters can get corrupted. You decide if you want that.