That is indeed what Oxford, say, typically requires from IB applicants. St Andrews technically states lower minimum/standard requirements for IB applicants (like many courses say they will allow one HL 5 standard, or two HL 5s minimum). But these days it seems St Andrews often has actual average entry tariffs similar to Oxford. So that implies in practice St Andrews likely is requiring considerably more than the minimum/standard requirements for actual admissions.
Anyway, that of course makes sense. Oxbridge educates something like 1.2% of full-time bachelor’s-level students in the UK system. And their admissions system is not “holistic”, it is very much about course-specific academic qualifications. The interviews, and where relevant special entrance exams, cause a little more variability around entry tariffs at Oxbridge specifically, the personal statement might serve that function a bit at St Andrews, and so on. But generally speaking it makes sense Oxbridge’s requirements, and maybe these days St Andrews’ real world requirements, would be sufficient to get down to under 2% of the UK applicant pool.
Since the “top” (as defined by US News and such) US colleges are mostly “holistic”, there is really an apples to oranges problem with comparing them to Oxbridge and the like. But I think it is worth noting that to get to the same 1.2% of the US pool of full-time four-year bachelor’s level students, you would need to include something like all of the Ivy League, the other 7 or so universities typically identified as equivalent to Ivy League universities (again by a US News-type framework), and a few of the “top” LACs. And actually, quite a bit more if you took out “hooked” admittees with no UK equivalent, like recruited athletes.
And, not surprisingly, the typical academic profile for “unhooked” admittees to those “top” colleges making up 1.2% or so of “unhooked” students is very high, and very rarely achieved. Online conversations self-select in ways that can distort that impression, but depending on your exact definitions, the “average excellent” applicant in the US might well have an academic profile that puts them into the top 1-2% of the US applicant pool overall.
But because US admissions to these “top” schools is mostly “holistic”, there is considerably more variability around admissions decisions for a given set of academic qualifications. As a result, the “average excellent” US applicant who is in the top 1-2% of the general US applicant pool might well be very likely to at least get an interview at Oxford (at which point depending on the course you might have between a 1:2 and 1:4 chance of actual admissions), and get an unconditional offer from St Andrews. Because they in fact are in that rare percentile range by academic qualifications that those universities are looking for.
But, there is no guarantee such an “average excellent” applicant would have similarly good odds at their favorite “top” US colleges, and potentially could be admitted to no such “top” US colleges if they ended up not scoring high enough on non-academic factors. Something that essentially cannot happen in the UK system.
I understand the dangers of overreading this situation. US “college prep” students are mostly prepared for the US college system, not the UK system, and as we have discussed that can be a problem for some US students. Still, as we have also discussed, I think this is a situation that with some care can at least be partially addressed by US students who go beyond a “typical” US college prep curriculum.
And absolutely, that in some sense means you might actually be distinct from even the typical “average excellent” US applicant. Meaning being a top 1-2% IB student in the US is rarer than being a top 1-2% AP-focused college prep student. Not necessarily better, but following the IB path to that percentile means you have been prepped in a different way.
And so IF you are that specific sort of “average excellent” student who has gone beyond just a typical AP-focused college prep approach, I don’t think you should necessarily be put off by the different challenges you will face at a UK university. But it will definitely be different, and not at all something you must want, even if you could have it.