I'm wfp now but when I was trad I never had problems in 16 years. A couple of lucky escapes in the beginning, but you learn from them. It's all common sense. It depends on a combination of surface type, surface wetness, algae, ladder angle, both stiles evenly resting on the wall, slope of the ground, weight, and condition of your ladder rubbers/stoppers.
I probably wouldn't have entertained putting a ladder on those quarry tiles. Spikes are a joke on hard surfaces. It'll wreck the surface. And I don't see the point of them on grass as you can dig in without them. Ladders are perfectly safe used properly.