I think it's the labels that irk some people.
It is the label that irks me and the idea that it is new.
It is mother led. If I go to someone's house and they ask me if I want broccoli and stilton soup or pea and ham soup, I will go for the second. I am lucky in that I eat most things but I don't really like either and as I am hungry and polite and that is the choice I opt for one. I would be a bit miffed if the hostess then told everyone 'exotic chose the soup today'. If I had really opted for what I liked I would have carrot and coriander-the hostess chose the soup. It is the same with the BLW-nothing to do with the baby and if someone gave the baby a choice not sanctioned by the mother there would be hell to pay!
I don't know where you get the idea that all babies were weaned at 3/4 months and they all had purees. People did there own thing and it was a mixture. I personally like my soups pureed, I much prefer them to ones with bits-how on earth do you know what your baby likes unless you give them both? You also cannot feed a baby more than they want to eat-they won't eat it.
It isn't difficult-the aim to to get them onto the family diet as quickly as possible-how you do it is unimportant. But unless the baby is advanced enough to sit up and say 'I would like my potato unmashed and I don't want the fish' it isn't baby led!
It is a trendy fad until the next one appears and meanwhile people just quietly get on with it without giving it labels. I feed them the same as the family-some is very solid, some is mashed, some is pureed-but so it is with the rest of the family.