The Gleeful Grognard wrote:
Leap, grab edge, ascend to top of ledge. Envision it more as freerunning than climbing.
This. When I think of Mantle I think of how Destiny 1 did not have "mantle" and you could clip your toe just under the ledge and you were gonna glide to your death, but in Destiny 2 if you were more than halfway above the cliff you were able to grab on and pull yourself easily onto the ledge.
https://www.youtube.com/watch?v=L9CQLPbyXGU