I see and agree to your points completely - if they are used just for potty training, then they have a valid function.
I question why a company makes such a product (Size 3) that fits a child of 16lbs to 28lbs which equates to 2mths old to 4years with the average being 16mths old. Companies do not make products that do not sell, or that they have at least done some market research. The conclusion that I come to, and I may be wrong, is that these companies want babies toilet training to be delayed as long as possible - after all, they make money the longer a person uses their products. These same companies advertise the message that as soon as a baby learns to stand, they don't want to lay down for a change, so the parent should support them in using pull on diapers.
To me, that creates two problems :-
- if the child is upset at having to lay down to get its diaper changed, it will associate the inconvenience it feels with diapers which might make toilet training a little easier.
- if a child is used to diapers being pull-ups, that is teaching the child that there is no difference between a pull-up diaper and pull-up underwear.
I trained my two using cloth training pants - and yes, there were a few (pulls hair out) messes and tantrums, but due to the instant feedback of the cloth, my two (boy and girl) trained in 2-3 days. I don't think that in a nappy pant even with the wet feel, that the feedback would be so instant. Being IC myself, I lined on of my own diapers with a wet-feel pant, and it was not that uncomfortable - as opposed to thin cloth and no plastic pants.