Having bagged both mountains on several occasions I tend to think of them both to be on the same level as far as physical effort required and even time required to summit (for summer ascents). As you know, the Whitney main trail is a walk up on a trail. Langley is mostly a walk up, but with some easy scrambling part-way up the summit "block". There must be a hundred different use trails on Langley though, so I often just pick one that seems like it is going where I want to be headed on the mountain.
But to answer your question, in my opinion they are nearly the same effort and time -- but that is because for me, the scrambling on Langley is short and easy, and probably even avoidable if one were to try to avoid it. The sand wasn't ever and issue for me since I just stayed on the use trails. Yes, there is the annoying, yet required dip from New Army Pass down to Old Army pass.
Please remember that the relative level of difficulty will be different for everyone.
