That he's going fast?
I'll cautiously put a foot into this thread...
My first vehicle was a Jeep (worked for the $$ for it, fully maintained it with my hands). If I had a video camera back then, there might have been a few spots similar to those in the vid. Puddle splash'n / mud spray'n. It didn't seem totally out of line to the vehicle nor to the landscape. Pushing the limits on occasion, perhaps.
As for your question as to speed... It may seriously depend upon the trail being traveled. I find trail speed (Colorado mountain trails) to be in the 3-7MPH (GPS measured) range with 10MPH being considered "fast". Not all trails are like this nor do all drivers travel those speeds - though the common groups I meet up with, do.
I assumed this is what everyone here does with their XJ.
I'd say, ride along (even if as a passenger) with a reputable trail group in your area to see what a trail ride is like. Check out some YouTube trail ride vids (for what would be solid, scenic or technical, rides - not the vids showing only rollovers & stucks).
IMO, I think your assumption of what's going on is not what the majority is like.
Any clubs or groups near you (or within three hours one-way for a weekend away)?
I did a quick YouTube vid search and this popped up. It seems similar to what I've been used to (trail types, speeds, group activity - spacing, someone out taking pix or spotting a vehicle through a difficult spot, etc).
Trails, to me, have two attractions: Enjoyable scenery or on-trail technical obstacles. To each their own to enjoy what they wish.