I will try to my best here.
Yes, it takes longer to cross the thumb over to release the safety. But it is free time.
No such thing as "free time" when you are deploying a gun for defense.
The safety release is not the rate determining step in getting the pistol ready to shoot. It doesn't slow the process down because there it takes longer to raise the pistol to shooting position. So there is some spare time there that can be used to cross the thumb over and back without affecting the total time to sight on target.
Are familiar with "shooting from retention"?
This is the idea that you pull the gun from the holster, and because your opponent is already on top of you, you start shooting with one hand with the pistol close to you body.
There is not extension or sight picture. You are putting rounds on target as fast as you possibly can while making space, deflecting attacks, etc.
There are some good videos on it.
ETA: found one after quick search. Start at 3:40
ETA2: a better one probably:
Maybe could fire the gun with the thumb crossed over but I wouldn't do it. And why would I have to? As I said above, I have the thumb back in correct position before the gun is in position to fire.
Because when the chips are down we don't get to pick how it plays out.
Everybody's plan is perfect, until it meets the opposition. Then all bets are off.
The bad guys don't play by our pre-planned choreography.
I know I can't convince you guys the gun is secure while the thumb flipping is going on. All I can do is tell you that is my belief. I am not going to drop it.
K, but you have lots of people with really good research and experience here trying to explain.
The thumb is not on the wrong side when the gun leaves the holster. It moves over to the opposite side during the rise.
If I am hearing you correct, you are disengaging the safety before it leaves the holster, right?
I am no tactical operator but that sounds like you are disengaging the safety too soon, to me.
As far as handling this with one of your students I would suggest you consider it on a case-specific basis. If the student is managing the process well, then what's the problem?
Safety, mostly.
If they are taking the gun off safe before the muzzle is down range, that represents a valid safety concern.
I have seen people rope steers and dally with their thumbs down. Lots of thumb-less cowboys would tell you that's not a good idea.
And let's face it, I am not the first person to face this issue. Over the more than 100 years the gun has been in use, many leftys must have developed sound draw technique with the standard safety 1911s. At least I would think so.
While you are correct, that doesn't make it any better.
The Navy still trains ALL recruits with right handed holsters. Doesn't make it a good idea but they figure it out. Obviously they would be better served with left handed equipment.
Before ambi safeties, I would bet that the 1911 was not a preferred side arm of lefties.
For what it's worth, you are welcome.
THR is hands down the best firearms knowledge website in existence and the folks here genuinely want to help and many of them really know their stuff.
Good luck out there.