Bolding is mine....
That is clearly a matter of opinion. I develope adhesive capsulitis in my shoulder and don't have the strength, nor should I use my shoulder to the extent to 'wheel' myself arould the park in a wheelchair (at the advice of the Dr's). If you are not used to using a wheelchair on a regular basis, it is very tiring to your upper body!! So I disagree, and say you lose a TREMENDOUS amount of independence.
Not necessarily - If the boy walked between rides and, therefore, was allowed to run up to a character and walk next to a sibling to talk, etc, but had a wheelchair when they were standing in lines, where they are moving slowly and he had no place to choose to go anyway, he could sit down there and rest his knees. He could also have that chair ready and waiting while they are waiting for parades, fireworks, and night times shows, where he also is not moving from place to place. This ability to sit at such times can allow him greatly increased stamina and freedom from pain (and therefore more independence) at times when he can use it!
I, too, cannot push a wheelchair all day (I have an ultra light weight, so not heavy) due to shoulder problems, so I push with my feet as often as my hands. I just had to find a chair that worked for me. And before I was unable to do so, I pushed my chair as often as I sat in it, and I found that the decrease in pain and increase in stamina was liberating. I went from housebound to Disneyland 2-3 times a week.
But I agree that if the mobility device is not fitted to the situation and the person carefully, then it can make the situation worse.