You are making an unfounded assumption. In the wild, a hen that hatches 20 keets and manages to raise 3 of them is considered a success. A domestic hen that hatches 20 keets and manages to raise 3 of them is considered a terrible mother.Susceptibility to predators is not on the same level as maternal instinct.
The question is of the strength of a guinea hen's maternal instinct, not entirely on her ability to pick a protected nesting spot although important.
So, on the question of maternal instinct, wild guinea hens tend to have a stronger maternal instinct than captive bred guinea hens.
Today I had a wild turkey hen show up with her 3 poults that were at least a month old. I guarantee you that she hatched more than that to start with. She is a success story for having raised 3 poults to their current age. She would be considered a terrible mother for raising so few had it been done in a domestic situation.
I had a turkey hen that successfully raised 14 poults last year. She had an advantage over the wild hen because her and her poults were isolated to a grow out pen for the first two weeks before they were allowed into the general population.
Your assumption that guinea hens in the wild have a stronger maternal instinct than domestic guinea hens has not been established by any studies that I am aware of. Both the wild and domestic hens would have to be observed under identical situations for any such study to have true value. It would also have to be conducted by an impartial observer to prevent false conclusions. Whether a hen is a good mother is based on more than maternal instinct. I have domestic guinea hens that have very strong maternal instincts. If allowed to raise keets in the wrong situation they could be considered bad mothers.