Design, as in functionality, is pretty important. Design as style, less so. It really depends on how much of a range hit one gets with the desired camper compared to a more aerodynamic one. Aerodynamics matter a lot when towing long stretches without chargers, or on long hauling days where the last thing you want to do is stop a fourth time. When charging is closer together or camping is relatively local, functionality starts to matter quite a bit more.
As an example, I have a front-mounted bike rack on my Airstream that holds the bikes right over the propane tanks. They make a noticeable difference in consumption and probably cut my range by about 10-20 miles at highway speeds. However, mounting the bikes there also keeps them out of the camper allowing us to use it for stops on the road. It keeps dirt out of the camper on the way home, etc., so I tend to use that rack anyway most of the time. In my case, though, I have the flexibility of deciding to put them inside if there's a long haul ahead and I'm worried about range.
There's a balance between aerodynamics, functionality, cost, and style that is pretty personal to each buyer. And I'd say that with my 90D, aerodynamics were significantly more important than they are with my X LR++, though they still probably top the list for me personally.