I was in Leon, GTO just 2 weeks ago and I had absolutley zero issues. I went out at night drinking with some suppliers, ate lunches and even walked the streets next to the hotel during the day and evening.
Even ate tacos at 1am after leaving the bar !!
Of course, I do not walk into the colonias or barrios looking for "culture immersion" either !!
So, it is safe as long as you know where you are going.
Living next to Juarez, I ABSOLUTELY REFUSE to go to that city.