The reality is that for very competitive courses at the very top universities, not everyone who has the required predicted grades gets an offer. Therefore, they are sifting and binning people based on certain criteria. It is daft to suggest that things like predicted grades or GCSEs or other factors make zero difference.
Some universities might group candidates according to A Levl predictions and work down the list..so those with 3x A Star are offered to first etc.
Some won’t have specific GCSE requirements but will look at the overall GCSE picture and use that to group candidates as well as GCSEs.
The other thing is to remmeber GCSEs are looked at in context of your schooling and postcode etc. So certain GCSEs will be much more imoresssive to admissions departments if from a state school in a deprived postcode than from a top independent school.
For most universities and most courses, if you meet the A Level predicted grade requirements and have the Maths and English basic GCSE requirements, you should get an offer. Most universities and courses don’t have enough applicants to be turning people away who meet their grade requirements…especially as not everyone they offer to will come. BUT some very competitive courses like Economics at certain top universities will have far more people apply who have grades predicted at the required level than they can offer to. So they have to sift somehow and GCSE profile, personal statement, possibly interview can all be part of it, alo g with having targets of offers to make according to international or domestic status, and probably state/indeoendnet / contextual candidates.
In short, for most places and courses, that 6 at GCSE won’t be a hinderance at all. For a few courses in a few places, especially if you’re from an academically successful school, it won’t help, but it probably won’t make a real difference if everything g else about your application is strong.
Those making sweeping statements about it mattering or not, need to remmeber that a lot depends on which course and where exactly someone is applying. Some places certainly won’t be bothered by a 6 at GCSE English. For others, it could be a factor that works against you.