An other thing to consider with decrease attribute spells is what exactly is the effect, and what you are expecting.
Dropping strength to 0 is a great way to reduce a mook to a floor slug for sure. But it doesn't stop him from using implants to call for help wirelessly.
Then there is the range (touch) which means you have to be right next to the target...... if your stealth abilities are good enough to get that close, they are probably goid enough just to sneak by him.
Then there is the fact that these have to be sustained to be effective.... which means for every mook you drop with a decrease attribute spell, your mage is taking a -2 DP to everything.... 2 mooks? -4. 3 mooks? -6.....
Yes you can get around this with sustaining foci and focused concentration, but that is a fair investment for such a niche spell, and will only offset so many spells. (Well, 1 per foci and FC).
Some days the solution is not magic at all, or a more direct magical approach is more effective/less resource intensive.
But if you really want to go this way, targeting mental stats is the way to go. Reduce a mental stat to zero, turn the mook into a veggie

No brain, no movement, no using inplants or wireless to call for help.