Speaking as a parent of 1 slim and typically hungry DC and 2 quite overweight and absolutely voracious DCs, who have been that way since birth - it's easy to be laid back when your DCs are already more or less in touch with their own appetites. It's really, really hard when they aren't. And if I hadn't experienced DCs who consistently over-ate, I'd probably be yet another smug voice coming on to say that my DCs had open access to the fruit bowl, served their own portions etc and were fine.
Particularly for my DC with ASD, I do regulate quite a bit. They're always allowed to ask for seconds or choose their snack from a nutritious selection (e.g. fruit, oatcakes and cheese, veg and hummus, crackers with peanut butter), or leave anything too - but I do serve up smaller portions and am strict on only 2 snacks if it's a regular day.
There should be more support for parents with naturally heavier DCs, so often we are told by professionals to cut out McDonalds, when it's not about that at all, and then left alone to worry about leaving our DCs overweight and bullied or with health impacts, or equally bad if not worse, with an eating disorder.
Lastly, some of the relaxed parents possibly shouldn't be quite so chilled - on the thread by the worried mum earlier, there were a lot of posters coming on to talk about how they and their DCs are 'big boned" and "heavily muscled' so had significantly overweight BMIs. That's surprising, when bone makes up a small percentage of weight, and muscle is not going to swing you from healthy to obese unless you're Venus Williams or a hobbyist powerlifter..
So in answer to what you're saying, no I wouldn't personally let even my quite skinny DC eat 8 apples as it's expensive and a pain to replace - but it's really worth trying to let them have a chance of being in charge. We tried the Ellyn Satter method, it unfortunately didn't work for my ASD DC, but I think her approach of shared responsibility is a really healthy one, even if it leads to a little more pickiness or food waste in the short term.