The anti-sim and anti-early-study are standard UK instructor prejudices, which can be argued both ways.
If you have someone who has been a simmer for years, seriously, he will know quite a lot about flying - probably far more about flying
to places than somebody with a PPL
The sim won't teach the finer points of aircraft control but that doesn't matter.
Doing the theory early is OK if you have somebody to help you, otherwise just diving into the books is very sterile. Personally I disliked the PPL books (Trevor Thom) because they contain so much dross, but they have to be used to pass the CAA exams because of special terminology used
The point is that there is no formal ground school within the PPL so
whenever you dive into the books, it will be very tedious if you have to do it alone at home.
It is a good idea to check out a few schools, because they differ a lot. Some are friendly, some are not, some are disorganised, etc. Make sure you have a logbook so every trial lesson can be logged; they will all count towards the 45 hours minimum total time.