Hello, Sparky, and welcome to the Grammar Exchange.
In traditional grammar, those V-ing forms functioning as adjectives were called present participles (the term "gerund" was reserved for nominal functions). Nowadays, we tend to use the term "V-ing forms" at all times.
It's not that "praying man" and "laughing people" are unnatural — they refer to a usual or permanent (rather than temporary) condition.
I would be happy if anyone can explain why we can use the gerund before the noun 'people '.in this sentence as follows -
She could not leave her suffering people behind .
The sentence above refers to people who always suffered. You can make "suffering" temporary by placing it after the noun:
- She could not leave her people suffering behind.