While I don't have a newer LC with 8-speed, I am an engineer and enjoy postulating about various things.
I'm thinking the 8-speed is rougher, particularly in the lower gears, due to the lower first gear ratio. Not quite, but think of tractor trailers with their incredibly low gears and jerky take-offs.
View attachment 1415432
The 8-speed has a much lower first gear. Effective ratio with the diff, makes the 8-speed something like 15.8 vs 13 for the 6-speed. Add in the off-road oriented driveline, with transfer case, 4x4, and soft bushings, and that makes for a recipe for slack and jerkiness. It's incredibly hard to make something smooth against light load and slack.
That lower first gear could be a great advantage for hard core off-roaders, especially ones that fit larger tires. Funny enough, larger tires in itself might help smooth out shifts, as it puts a larger constant load against the driveline slack.