In the video, you have to hunch over the handlebar to keep the front wheel from lifting. That sounds tiring on an hour long climb.So the new geometry doesnt hurt you there? Can you think of what specifics about how a new bike is built would make it not as good at climbing dirt road or "minor" off roading?
When climbing dirt roads the really steep seat angles should keep you in a way more comfortable position than the old slacker seat tube angles.
I haven’t done much real mountain biking for some time now. For that kind of ride, I’d use a gravel bike, which has a geometry closer to “old school” mountain bike geometry than the “modern” geometry.