It's not the spell. It's not even the confusion (although the confusion is part of it). It's the low level spell that incapacitates non-rPois low-HD foes. The actual status condition is unimportant. The confusion is more than enough time to kill your foe, and even if they snap out of it early, just confuse em again. And if they're strong, confuse them and run away. You've got flexibility with Mephitic Cloud.
The reason I like Sticky Flame better is that with MC, you incapacitate your foe then kill them. With SF, you skip the intermediary and just kill them. Of course, I still learn MC since it's an amazing escape tool, but I use SF for general use. The downside to my "Vehumet DSFE" is primarily spell slots. That means no or little adaptability. With 1 slot on Flame Tongue, 2 on Throw Flame, and 4 on Sticky Flame, that's 7 spell levels spent right there. Since I generally turn off Spellcasting and in Trunk Demonspawn level very slowly, I tend to always be low on spell slots. Around the time I hit Lair Vehumet starts gifting me, so I want to keep 4 slots open for Mystic Blast and then spend my next 7 slots on Orb of Destruction (It's not great, but it works). To make matters even worse, I'm going to want Abjuration, too, so there's another 3 spell slots spent. By this point in the game, however, more and more enemies resist poison! Argh! So by this point I'm on the lookout for escape spells. MC is a good spell, but it won't help me escape from the kinds of enemies I actually want to get away from, such as hydras, liches (Boris, usually), high-HD uniques, demons, ranged attackers at edge of LOS, and probably several other nasties I've forgotten about. What with spell slots being so tight, I just can't afford to spend them on MC. I'd rather have Blink, and I dislike Blink.