Yeah I’d love to be spinning at my preferred 85 rpm cadence all the way up a 10 km Alpine pass with 12%+ gradients. But the reality is that sometimes I am forced into using a cadence well below what feels natural. Even much flatter routes often have short, steep climbs requiring a very low cadence. So to me it makes sense to spend some time training for these low cadence, high torque efforts.
As for high cadence, I find it useful to train sometimes well above my natural cadence as it appears to improve my efficiency at a normal cadence (it certainly makes a normal cadence feel more effortless afterward) and over the years my natural cadence has also crept up a little, which I think is a positive.
When I’m riding an event out on the road or mtb trail I feel comfortable at a wide range of cadence, which I put down to training over an even wider range. On a typical ride I might see a cadence range anywhere from 50 to 120 rpm depending on the terrain and bike.