^ a typical way is indeed to weigh the 3 A Levels more than the IGCSE’s. Furthermore in your example you have the rather extreme case of someone have 4-6 A’s at A-Level, when most students will have 4 AS and 3 A2, although clearly for top schools you see 4-6 AS and 4 A2. However, OP doesn’t have A-Levels so the point is moot.
5 igcse is the minimum. In other words, no, it’s probably not enough, unless the student has other exceptional qualities. But if that student shows s/he can handle a full A-Level program and get A’s or the equivalent in Ap’s and get 5’s ( 7-8 APs over 2 years - typically, 1 A level = 2 APs, 1 AS = 1 AP) then it wouldn’t matter much whether that student has 5 or 8, especially is the SSR explains that taking the minimal 5 is school policy.
This sentence should be qualified with “for students who wish to study STEM in the UK”.
If your goal is to study American Studies, or Law, or PPE, then the above igcse’s are not “core”.
For the US, core subjects are: English, Maths, Foreign Language, Science, Social Science/History; an art (music, orchestra, photography…) class is considered good and can be a requirement for some universities too.
26:
Yes, Northeastern only requires the TOEFL + national boards (igcse+ ALevel for instance), as do NYU and Elon. All three are excellent universities.