Is it possible for your average good student to get into Harvard?

Well, we don’t know what your 4.9 weighted GPA really means.

But even if we assume 4.0 unweighted in hard courses, you should assume that most admits to super-selective colleges have something extra, whether it is an earned achievement (e.g. some top end achievement) or unearned attribute (e.g. legacy), as well as something compelling in the hard-for-applicants-to-know-how-they-compare essays and recommendations and being what the college itself is looking for (some such things are stated publicly, but others are not – at the very least, check their public statements to ensure that you are not an obvious mismatch).