Volume of boats if tough to compare. The L karma has 103 gallons, but a lot of that volume is above the water line. What that means is that when you go through a hole, or go into features that would submerge a smaller boat, the extra volume will keep you on the surface instead of subbing out.
When you are paddling, you don't feel like you are having to move around a huge boat, but when you hit a big seam or hole and you stay on top and upright vs. getting subbed out and flipped, thats where the volume helps.
I think volume and length paradigms change over time. Back in the day boats were long and skinny, and people thought short boats were a novelty. Seems to me that creekboats went smaller, and now many are going back to longer boats and bigger volumes. Its different than boats of several years ago, but the notion that somehow a larger boat is worse to paddle or harder to paddle or only good for expeditions is the wrong way to look at it. Its all about how the new design paddles.
Of course the karma L was really nice to have on the overnight I did this year. Plenty of room, and it paddled really well loaded down since its got the extra volume to not get to loaded down with extra gear.