This research is biased toward 'male/female' traditional parenting, but supports other research I've read showing that having two parents who function somewhat differently is ideal for development. (Or at least 'two types of parenting' - single parents play both roles, and often have other caregivers doing both as well.)
Other research has found that the most emotional resilience comes from having parents that are:
a) both warm
b) have different degrees of 'in there' responses to stressful or challenging experiences
Having two parents who leap to help/comfort/encourage/rescue/etc. ends up creating emotionally fragile children - the 'attachment' orientation at that level should be tilted more strongly toward one parent. Kids need both to know they have someone who will back them up promptly, and someone who trusts them to figure it out and carry on. The 'oh-you-poor-thing/let-me-help!' and the 'shake-it-off/you-can-do-it' are both part of what we need.
Just like modern attachment research is showing that the strongest attachment function doesn't have to be the mom - or even female - (can be a sibling, dad, grandparent, other caregiver), I suspect that this 'dad/male=gives space to explore' thing will eventually be shown to not be dad/male dependent. Certainly ep and I trade back and forth on who is in there and who is 'buck-up' on any situation, and for the different kids.
For example, Miss R is a daddy's girl. She usually doesn't even want me to be the in-there parent, comforting and fixing boo-boos. She wants daddy to do that. Which daddy does. So, for her, I'm more the 'rah-rah/good job/try again/you can do it!' parent. But if daddy is not around, then I take both roles.
I wonder also how the Montessori process feeds into this, as it encourages warm and affectionate interactions, but leaves plenty of space for the kids to explore on their own in a way that feeds into both accepting challenges, and understanding the process of overstepping one's skills and reassessing/trying again (American Montessori allows kids to take out work out of sequence, so they discover the concept of assessing where their skill boundaries are, and pushing those appropriately rather than jumping too far ahead - the sequences are built very carefully to support that process).
I like the balance in the theories. We don't just need one thing. We evolved with different kinds of relationships with different kinds of people caring for us.
Interestingly, in different cultures, the same concepts apply differently - both parents start out much more 'in there' in many Asian cultures, but with age they both step back a little more and then a little more - but also expect to function differently in adulthood, as well, so the pattern 'fits' with the larger relationship pattern over time as well. Where the resilience may be technically lower on the individual scale (by having had two very 'in there' parents), the long-term impact is not necessarily negative, because there is the expectation that of course you don't have to handle life's challenges on your own, that's what family is for! So while this research is valid for American culture, it is likely to not be applicable 'directly' across cultures. Extrapolation, yes, direct application, no.