There are ways. It can be done. Ch'lana was wounded, and vulnerable for the better part of a round. But every time she tried to kill him, someone shot at her and forced her to deflect.
Think of the duel between Qui-gon and Darth Maul. Maul landed a melee strike, which stunned Qui-gon. Maul was then able to dispatch him easily, as all Qui-Gon's other powers came crashing down. Jedo duels tend to be long affairs, if the Jedi are well-matched, but also tend to end very quickly when they do end because someone gets stunned our wounded, and all their protections end. Their opponent is then able to dispatch them with ease.
Most Jedi powers are very powerful, but they also build MAPs at a prodigious rate. LSC is a two-action ability, before they even take a swing with their sabre. Control pain is one action. Combat Sense is two actions, etc etc. If a power has, for example, Control and Sense, then using that power counts as two actions. Keeping a power Up means those MAPs will apply.
Jedi are very good at defending against projectiles and blasters. Where they are weak is area effect weapons - grenades (if you can get it to go off), flame throwers, slug-thrower shotguns, neural inhibitors (think tazer), scatter blasters, repeating weapons, and similar things. They do have tricks and powers for dealing with those (absorb/dissipate energy, control pain, resist stun). But area weapons bypass their strongest defences, and they must incur additional MAP's to counter those.
