Not sure what you're seeing...
Original Prototype:
From today (via the video posted above)
View attachment 938291
I know the camera angles are slightly off...but are you just complaining about the height-wise "thickness" of the black bumpers front and rear? You're probably right that's for aero, and probably also crash/compatibility regulations. Just about every factory-truck on the market has similar metal and plastic bits nowadays, likely also for aero and crash compatibility.
For off-roading: aren't the front and rear bumpers like the first and easiest thing off-roaders replace to enhance their angles? Looks like those off-roady tube bumpers are a few hundred dollars online. Such a low-cost and probably easy DIY makes sense as an after-market replacement rather than making every Cybertruck have the worse aero (range, noise) and crash performance.
(edited for type-o's)