There's not a large enough sample size to tell whether a given spell was more or less effective or why. You're only going to be casting a handful of spells per combat on any given enemy.

And no, I'm not interested in keeping things as-is, because I have explicit developer quotes confirming that the pre-remaster rules are purposefully balanced wrong. i.e. The devs say casters who fail to avoid strong saving throws will not perform as intended, and are playing the game "wrong". This is in spite of the fact that the rules as written do not allow them to learn these saving throws, relative or …