Yep, all those things mashed together, Yellow, with contextual factors allowed to modify them. By success I mean receiving an offer. I know a bit about science applications because ds will be doing one this year. maths and physics desummon quite viciously on the basis of their pre-tests, irrespective of exam outcomes in GCSE and AS.
Yellow, I admire your idealism, but frankly it is idealism. Your dcs can make any kind of choice they like, but a reminder might be in order that nobody ever seems to reject their second-choice college if it offers and their first choice one doesn't. There is therefore SOMETHING to be said for knowing the odds; if you choose to ignore them, that's your choice.
BLUNTLY, and all over again, everyone is at liberty to choose in whatever way they like, but some might like at least to be aware of the effect they are having on the likely outcome of the application. That just seems to me a basic right - and schools in all sectors are STILL directing kids haplessly to oversubscribed colleges BECAUSE neither they nor the kids really understand the interior workings of the system. If you really like a college you might be willing to take the risk, but lots of applicants are still jabbing a pin in a list when they might just as well put in for somewhere else they like just as much. This isn't 'playing the system'. It kicks in when the candidate doesn't mind desperately about college choice, but about Oxford - and this IME is most of them.
I am not saying there are ANY soft ways in - just less ridiculously hard ones. You still need great GCSEs and predicted A*s and As to be shortlisted for ANY college, and then you need brilliant written work, and a good pretest score.. and great interview scores, everywhere. But at some colleges there are 50 people who have those things competing for 10 places, and at others there are 25. Yes, there's reallocation; yes, there are second interviews, but even so your chances are still numerically worse.