To put in context if I did a MH run with my guild of geared players who know what they’re doing, we clear it in roughly 2 - 3 hours assuming little to no wipes.
If I did that same run in a GDKP with everyone being at top gear, top spec, top skill and knowing all fights we can clear in 1 and a half hour or less especially if the group is stacked.
Difference is that in GDKP runs, you can customize the group to be the most effective possible for clears where as in traditional guild runs you have such a wide mix of guildies/classes and it always won’t be optimal unless you’re running world first stuff.
In this context, it makes more sense time wise for people to do GDKPs because they are guaranteed a faster performance.