Fixing the date for Easter is difficult. But it is based on the date for Passover, since according to the Scriptures, Jesus was crucified on the afternoon before Passover began (at sunset).
The Jewish calendar has a lunar basis. The Christian calendar has a combined lunar and solar basis. So Easter and Passover don’t always coincide.
But it’s not up to some jerk in the Anglican Church to tell us when Easter is. All this will do is spread the divisions among churches still further as to if and when Easter should be celebrated. The opposite of what he proposes to accomplish.
The Anglican Communion is the 3rd largest Christian denomination in the world—after Roman Catholics and Eastern Orthodox. Anglicanism in general, and Archbishop Welby in particular, are VERY conciliar—that is they work through councils and broad agreement. I am certain that the Anglican Communion would never agree to changing how the date of Easter is ascertained unless at least Roman Catholicism went along—as well as representatives from other Christian denominations.
Welby would probably want the Eastern Orthodox on board too....and since this is an ancient disagreement, it has little chance of being mended any time soon.