I think even as of this date, Musiala is better than Bellingham. He deserved to win the Kopa trophy as well. Bellingham is rated higher than Musiala in the eyes of many people because he was on the transfer market recently, and there were many teams fighting to sign him.

Musiala beats Bellingham in many technical abilities, and I think he will outperform Bellingham in his prime.

Bellingham

Musiala is better at close range dribbling in tight spaces. If he starts capitalising on that skill with a better final ball/ shooting I think he might have a higher ceiling.