Here's the thing, The telegraphed lunge punch defended by a wrist grab looks pathetic to anyone that has ever been in a real fight. No one cares what principles you think you are developing, the stuff doesnt work when the chips are down.
Whether the punch is speedy or not, GET OUT OF THE WAY! Instead of trying to grab their wrist, go for the shoulder; once you have your hand on the shoulder, it should be (relatively) easy to find their wrist. Throughout all of your technique, you should be MOVING.
Admittedly, seeing someone slooowly throw a punch and have their wrist grabbed on the second try by someone with poor timing can look pretty sorry...
...but you have to start somewhere. Some of the people that walk through the door of your dojo will be out of shape or klutzy, or have no experience with fighting at all. If you don't work with them, they probably won't get a chance to improve.