I do think there is a gap, but that's naturally expected and there needs to be some sort of gap. I didn't find there to be a huge gap between GCSEs and A levels personally because I've always been an independent learner and I did some AS levels in GCSE years so had more time to get used to them. Here at Liverpool, as syllabuses vary, they do quickly cover the basics at what some where taught at A level before digging a little deeper (e.g. we learned about protein folding and 3ry structures all over again!) so they do make sure everyone is at the same level to begin with in first year.
I think the pass rate for some of our modules varies between 80%-100% in years 1-2. So it's not bad really (I've heard worse pass marks at some vet schools when they messed up their grade boundaries). From those who fail it's usually those who don't put in the work (and think "A levels were easy, let's see how little revision I can do to pass uni exams" - believe me some smart arses did think that) , have had family problems/are bereaved or revision methods just didn't work for them. And the failure rate for the whole year (ie people who failed resits and had to resit the year again) was around 5% or something like that, but I don't know the circumstances and whether they were just having a hard time with things outside of uni. So in all likelihood, you will be passing every year
There's less pressure to do well too as you don't need to be top of the class anymore and even those who scrap by qualify and find employment.
I do think it is flawed how the knack for passing A levels is to do with learning
how to answer questions, though, as you said, you need some knowledge. At Uni I found this still to be the case somewhat (with short essays) but not as much as for A levels, which is as it should be!
For me past papers tell me where my weaknesses lie to be honest, and gives me a kick in the backside if I don't do so well
So in that sense I wish we had a bit more past papers - the grass is always greener on the otherside perhaps
And that's where uni comes in - where you can learn to actually put your knowledge and skills to good use (e.g. treating animals). GCSEs and A levels are just a hoop to jump through to get to a career where you will be learning actual skills. Exams teach us how to learn, memorise and recall information, which is important for a vet too (though most of what we learn at uni in years 1-3, aside from anatomy, will not be that important for being a vet).