First off, I want to thank the OP for having the courage to admit a mistake and open this discussion so we can all learn from it. Anyone can be overpowered. We try hard not to be surprised. But that is the definition of an ambush.
A lot of cops are indeed shot with their own or a partner's snatched gun. Security holsters can help but if a perp can't get your gun out, neither can you.

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Reserve Officer 9yrs