I don’t believe most (Over 50%) MFL grads are privately educated but even in 2013 (where I found stats) it was 34%. This cannot be lower 7 years on as the state school dc drop languages like a stone as soon as they can. Many state schools don’t promote languages but of course some are wonderful. Just not enough. Tiny classes are not usually allowed in state schools and a lack of choice of languages is also a concern. These days just French and Spanish is the norm and just one of these at GCSE is normal too. MFL A level entries keep going down, but in private schools they are steady. However privately educated students make no difference to the university experience. It’s possible to find like minded people at all universities. Bristol, Cambridge, Durham, St Andrews and Oxford have always been private school heavy but that’s no reason to shun them. Go to the best you can.
The bigger problem is competing with native speakers. They come from any type of school and, if their parents are MFL teachers or similar, they definitely have an advantage! As they do at A level.
My DD had early decisions in October and a March decision as I recall. No, universities do not all wait until the January deadline before offering. But I would wait until all offers are in before making a decision. It’s only Oxbridge where there’s any question over an offer (unless a dc is really punching above their academic weight!) because universities need the decent students and there are not enough of them.
I’m not sure when the deadline for applications is in Jan nor when Oxbridge send out offers but it can sometimes be January although mostly before Christmas I think. I don’t see any advantage in not putting every university down at the same time. They don’t know where else you’ve applied but they will guess Oxbridge with an early application. By receiving an early application, they know you are good!
DD did get into Oxford but an A level result went awry! Hence Bristol as insurance. I can honestly look back now she’s successfully on her way into a very competitive career, that it made no difference to her. Intellect and ability to do well wasn’t fully represented in her A level results!