I tried creating a new course with the new Explore. I usually do this by mirroring the AllTrails path and I keep that downloaded while traveling, just in case. The old Explore tended to overestimate elevation profiles by 20-30%, but the new one seems to underestimate by over 50%! That is enough to be almost unusable for hiking or backpacking, and enough error to actually be dangerous. I double-checked by editing a single point in the course with the old Explore app saved on an old iPad, and sure enough, by editing one point, the elevation profile was mostly corrected. I say "mostly" because there seemed to be a cliff created (far from the point I edited), and I've seen that behavior before in the old Explore app. I usually also go move the cliff point and it self-corrects but I didn't do that this time.
Here is the AllTrails path, the new Explore course (note that it doesn't show start or end, either...another bug I guess), the old Explore edited course, and the actual activity (slightly low as I paused and forgot to resume for ~0.20mi). AllTrails lists the elevation gain as 1627 ft. The Explore 4 calculated course elevation gain is only 799 ft. A single point edit in Explore 3 and the calculated elevation gain is 1609 ft (but note the "cliff" which I'd have to edit again to correct). Finally, the actual activity measured 1608 ft gain. FWIW I tested the new Apple Maps route creation and it estimated ~1700 ft but was missing trail segments so the route was wrong/longer than it should've been.
My best guess is the new course low elevation profile may be related to the loss of 20ft topo contour information in the new Explore TopoActive maps...and another reason the new Explore app needs changes to be acceptable for use.
