Applying for a foundation year while going to a private school.

I am a year 13 student looking to apply for mechanical engineering at uni, however my UCAS predicted grades aren't high enough for most of the top russel group universities with direct entry. Because of this, I am considering applying for a foundation at Manchester (and potentially another place), where I am a grade above the requirement to apply. Passing the foundation and studying mech eng at Manchester would be better long term than my best direct entry options, but I have heard that it is harder to be offered a place on a foundation course if you go to a good independent school, even if the course doesn't have non-educational requirements. To what extent is this true, for me, the course, and the university, and is it still worth applying for.

Presumaby you are aware that RG is totally irrelevant for Engineering? I would seriously consider a non-RG with a placement year rather than this route.
What are your predicted grades and in what subjects?

AAB. I am aware that RG isn't too relevant, but the unis with good prospects I can apply for with good engineering prospects that I'm considering like Birmingham and Edinburgh are RG. And Manchester would be one of my best options too, but I don't meet the requirements. Regarding non-RG, Loughborough is one I am definitely applying for. How important would you say a placement year is? Would you say a MEng with no placement is better, or BEng with a placement

AAB. I am aware that RG isn't too relevant, but the unis with good prospects I can apply for with good engineering prospects that I'm considering like Birmingham and Edinburgh are RG. And Manchester would be one of my best options too, but I don't meet the requirements. Regarding non-RG, Loughborough is one I am definitely applying for. How important would you say a placement year is? Would you say a MEng with no placement is better, or BEng with a placement