2 and 3 are the major advantages of J1. Tax waiver is irrelevant. It depends on what to do, not what visa type you have.
Generally, if he can get waiver without problem, J1 is much better than H1b.
More advantages:
J1 has 30 days grace period whereas H1 has no grace period offically.
J1 holder can come back under visa auto-revalidation program after visiting certain Caribbean islands in addition to Mexico and Canada.