Those Legends are beautiful. There are days when I sometimes wish I was driving a set instead of my tubes from Jack. I think a lot of that is the aesthetic draw the Legends have.
Looking at the blueprints for each:
14' Legend Cats | SOTAR
There are two types of cats - gear haulers and play cats. Each of these models tries to be both.
I think the Royal Flush has more volume (carries more) and it definitely has a longer length between the outer-most D-rings (accommodates a longer frame and/or trailer frames).
The Legend is a smaller, sportier, sexier ride.
The Legend/WD packing advice seems to be "learn to go lighter". This of course will make any cat perform better, but do you want it to be a necessity?