Very strong, but not quite OP. Sadly, there's no option for that, so I voted balanced. Fast stabs would be okay if missing a stab had any sort of punishment. The amount of time you have from the end of one stab to hit you to the time another stab can hurt you after it misses is very small, which is why it's extremely difficult to force a glance the more powerful the stab since the glance-period is strict. There were a few times were I started my attack before the end of one stab missed and got hit by the next. Chambers are still an option, but they're less reliable than they used to be.
This makes it so that the only way to respond to a stab is if you manage to block it and punish the delay, or spam up close and don't let them turn it into you. If it's one centimeter off and misses instead, you're forced to block or you risk getting hit again. That's why I think a small delay after missing a stab makes sense if the early/late stabs can't be fixed; it also won't break stabs since missed swings are already much more punishable (still kind of quick if they "miss" aka hit an enemy, too, IMO).