Objectively, Madrid is a great move for Bellingham.
He's still only a nipper. Gets probably a UCL semi-final every year for four years, wins the league title every second year or so, gets to live in Madrid, get paid a fortune, gets to play with some great veterans and some great young players, then still has his pick of clubs if and when he wants to come back to England (including us, which moving to City would preclude).