Totally; it's my opinion. But, I see 1000s of students coming to University each year, and by 'well rounded', I mean they're better prepared for independent study at an HE level. They are also - overall - better prepared for self-management, financial challenges, looking after themselves, etc.
This is my experience across three quite different Universities over the last 10 years (a post-92, a red brick, and an ancient). I generally deal with students coming onto professionally qualifying programmes (nursing, teaching, social work, other allied health professions), where a bit of practicality, and managing juggling competing priorities.
Many young people coming straight from the hot-housed Private Schools really struggle, because their lives have been so regimented, and focussed on academic achievement (sometimes spoon fed), and are actually the group who often need more support.
We have services to support all types of student, and there's no shame at all in accessing it. I'm not judging any group, but given the question from the OP, my view is that State School kids, who do the IB, are best prepared at HE level.