As an ultra runner / trail runner I have to agree with the OP that I think this is definitely still a 'want to be athlete' device. If a device is going to die in an event likely to be in the 8-24 hour range plus, the Apple Watch Ultra is definitely not 'ultra', despite the monkier. To be fair to Apple, those of us really in the ultra watch market are a very small segment. There are loads of people hauling around Garmins, yet struggle to even bash out a 5km most weekends.
I'm definitely glad to see more competition in this space as Garmin has largely taken most of the market, leaving smaller pieces to Suunto, Polar and Coros, however Apple is clearly not ready to compete yet in the endurance market. I am however hoping that this new product pushes Garmin and the others to make some more innovations, as our market segment has been suffering 'intel disease' lately, where only incremental improvements have been made each year and vendors largely locking out new features by way of software rather than making genuine hardware improvements.
I'm sorry but from the initial vague specs released, I honestly don't believe the Ultra is really made for 'intense athletes'.