That said, anyone trying even a “long slung arm grab” is an immediate threat to my life, and to grab my gun you’ve just put yourself within contact distance.

Contact distance with a Silat guru fighting for his life is not a place you want to be.

Next, you need to get with a competent martial-arts instructor who will teach you the body moves to first trap, then dislodge the hand(s) of someone attempting a grab, regardless of which direction they attempt from. Strength can be beaten with good moves, and that maxim affects BOTH sides of a gun-grab.

Finally, you need to practice fast draw and load (most open-carry is done with an unloaded weapon by rule).

Finally, you need to remember that any attempt gun grab is an attempt murder, with YOU as the FIRST intended victim. An attempt murder means every attempted gun grab ends with a dead grabber, or it ends badly.

Based on my personal LEO experience, I would say that it takes at least 3 intense 3-4 hour sessions to gain the muscle memory to do all of these things correctly, and at least 3-4 hours refresher practice two or three times a year thereafter.

If you are open-carrying, you should probably get a “red-gun” for such practice, since few dojos will let you practice with the real thing.