I have two at selective schools, one tutored and one not. The DC who was tutored got a lot more out of than just 11+ prep, lots of useful exam prep, time management skills and strategies which have helped generally since the 11+ (DC now in year 8 ). My eldest DC, now in year 11 , wasn't tutored but was recently asked at school open evening by some prospective parents whether he thought tutoring was a good thing. He said that he thought tutoring was definitely a good idea (he is one of a very small number in his year who wasn't tutored).
Presumably he was home tutored though? In that, you didn't just pitch up on the day and take the exam?
I think the question here isn't totally clear. It maybe should be about whether children are prepared, whether DIY (still tutoring) or paid tutor, vs doing absolutely nothing and turning up on exam day with no preparation whatsoever. The latter is extremely rare I would have thought. Buying papers or question books and sitting at home doing them is still tutoring, and to me represents a sensible thing to do. You'd never enter any other exam unprepared, or if you did, you'd expect not to do as well as those who are prepared, so why do it for the 11+?