" it takes more time to help someone teach a core subject that parents are all over than to teach RS"
But I think that depends more on the type of school you work in, rather than the subject. From your other thread, I'm guessing I've taught in very different types of schools than you.
The schools I have mostly taught in, have been very high achieving academically, and the parents can sometimes want to micro manage all aspects of their children's education - it is not the preserve of the core subjects (which technically, RS is btw, as it is not a national curriculum subject . But equally, the school I trained in, the parent's couldn't give a nat's arse about their child's education, not even maths! So there was none of the pressure that you mention. I even remember one parent bemoaning what was the point of maths (at GCSE level), because "they never use any of it when they leave school anyway" But that was a very different type of school.
Parents' level of engagement will vary because of the type of school you are in, for some they will be interested in all aspects - like for example, in mine - every report had to be hand written and individual (even if you were writing 200+ reports for that year group), and every homework had to be a full substantiated homework - otherwise parents would, and did complain! But then there are other schools where parents couldn't give two hoots about school at all - that depends on the school, not the subject.
I still stand by the statement that I made from one RS teacher to another (potential) RS teacher, that RS is so bloody difficult / cinderella subject because there are so many different demands made on RS teachers, that just get dismissed out of hand, because 'RS is an easy subject' but without really knowing or understanding actually what it is we do!