I think the issue isn't so much the altitude change but rather the ascent rate. I don't imagine that the elevator is all that slow.
As a diver you may remember off the top of your head that water is 800 times denser than air. That would make an aircraft ascent rate of 2400' per minute roughly comparable to a diving ascent rate of 3' per minute. Short of a very rapid ascent to altitude, I expect that the question is just at what point you're supersaturated enough that you bend.
We had a local instructor about 10 years ago do a fairly conservative set of training dives with her students, then she drove to her boyfriend's house over a maximum elevation of 1,600 ft and got bent. There may have been other factors involved.
Maybe a bunch of repetitive ascents? The decrease in pressure at 1600' is pretty small - perhaps 6 to 7%. That's comparable to an ascent from 99' to 91' or 50' to 44' and taking 3 minutes or more to do it (3 miles at 60 mph on a road with a grade of 10%).
Other than having a deco obligation and having just arrived at your deco ceiling, when would you be concerned about such an ascent? Granted, deco calculations with no safety margin could theoretically have you returning to the surface still at the very limit for surface pressure, so that any further immediate reduction is too much, but is that realistic? I'm not a deco diver and I realize that calculations aren't linear, but how long a "stop" would be required at sea level before ascending the equivalent of another 5 to 10' of sea water?
are we just being worrywarts?
As a business, what you permit customers to do and what you'd do yourself are different things. Based on what I know (which may be incorrect or insufficient), I wouldn't hesitate to go to 500 meters or so on an afternoon following a morning of diving. I wouldn't run from a shore dive and immediately speed up a steep road, but I'd certainly do it at a reasonable pace. Get out of the water, deal with gear, get changed, maybe have lunch, and then a reasonable drive? If it takes 40 minutes to an hour that seems like plenty of time for offgassing.
FWIW, I've always been under the impression that the time to fly interval is conservative and based on the possibility of an unusual decrease in cabin pressure.