While the Undead is ripping out of Confine two fighters swinging 10s should be able to pump 100 damage into the undead no problem. Lets not even talk about Eviscerate.
With the Flurry rule, this would be limited to 60 damage (30 each; 3 attacks each of 10 over 3-seconds, that of the rip count), so said 100-body thing would still have 40 body left. That is assuming one of those attacks isn't nullified by "Magic Armor" (or whatever it's called in new rules).
I'd also like to point out that in your above "this is okay" example, those two Fighters are swinging 5 times each in 3 seconds which even for 1.3 is too fast. At MOST they could swing 4 times if you didn't start counting until the first swing hits (they would then have 3 seconds to attack once per second for a total of 4 attacks).
So basically it would take TWO Confine spells to kill this thing instead of 1 given your above scenario of two Fighters hitting a 100-body thing that their caster friend as Confined.
I'd much rather see a spell do 100 damage than immediately end the fight AKA Death/Prison/Most Gases/Bindomancy/Purify/etc.
You can still end the fight with those effects (and several others), barring an Immunity, and given fights likely lasting longer, people will likely look to end fights sooner instead of slogging it out with duel-like Flurry-fests.
In your above example, you can either:
1) Confine -> Into Eviscerate (or other take-out effect) - Fight is over in 2 seconds.
or
2) Confine x2 --> into Two Fighters swinging for 10 using weapons to kill monster over 5-6 seconds. -- Fight is over in 10 seconds (allowing for Flurry rule pauses in combat)
or
3) Use 1 spell that does 100+ damage (assuming no defense called) and combat is over in 1 spell cast.
