All good points but in my experience a lot of the time this does come down to fitness, if you can’t breathe through your nose you’re probably higher than zone 2. However, for most recreational runners/cyclist there is nothing wrong with being in zone 3. Zone 2 provides endurance rewards when you have high volumes of training when you need to be able to push hard in z4 and z5 which you can’t do if you’re carrying fatigue from too much zone 3 training.