Suppose two international students both have perfect GPAs, perfect SAT scores, the same extracurriculars, essays and recommendations. The only difference between them is that one goes to an ib school, and the other to a regular high school. Does the ib student have an automatic advantage over the other one when applying to something like an Ivy, and how significant would you say that advantage is?
Impossible to say.
There are so many more factors at play beyond grades and scores.
It’s only an advantage if you’re among the top 2students in the IB school. But it’s the same advantage as being in an externally assessed system, so A Levels, BAC, Highers, DEC… would all carry some recognition. All in all, unless your alternative is not externally assessed, there isn’t.
For international students the main factor is how much they can pay.
An advantage of IB is that you get some credits, but AP is more flexible in that regard.
In other words, all else being equal? Well, all else are never equal. So there is no definitive answer to your hypothetical question. Ivy League colleges, and its peers, evaluate applications holistically.