I suspect there is a certain amount of elasticity to how much exercise a dog needs (or prefers), as well as variation between individual, breeds, ages, fitness levels.
Ultimately, if your dog is physically healthy and mentally sound then you're doing ok. If you're dog is displaying stress, boredom or anxiety behaviours (excessive pacing, licking, vocalisation, reactivity etc) then you might want to reassess how much and how you are walking them. Just changing that may not be the whole answer - or even any of the answer - but can help as part of a wider change.
A dog that has low level stress because its needs are not being met may well be less able than normal to cope with specific stress, such as moving house, meeting children, seeing the postman etc.
A dog that is exposed to regular stress because it is being walked too often or in a way that doesn't suit it, may be the same as above.
If you're dog is generally happy, relaxed, able to settle and cope reasonably well with unexpected or ad hoc stressors, etc then you are probably giving him/her the right level of exercise (and other things).
If you want to walk your dog more often and doing so still results in a happy, chilled dog then great. Ditto less. There are plenty of reactive dogs for whom a few days of not being walked at all following 'an event' would help lower adrenaline levels down to a point where they can once again start to cope a bit better.
Collies are an interesting example because I see a fair number that have excessing nerves or anxiety on a walk and wonder if this is because the frequency or manner of walking does not suit them. In fact, now I think on it, I cannot recall ever meeting a collie that wasn't nervous or anxious in some way but they must exist. Typically their neurological physicality is always used as the 'extreme' example in texts I've read (e.g. highest levels of dopamine receptors of all breeds) but this may be cliche or laziness on the part of the authors, because of their reputation as high-demand, so your experience fucks makes an interesting comparison.