I think it doesn't do Bellingham justice to just rate him based on goals, as he played much different roles for Dortmund and Real. Of course he will score more as a 10 (or more a 9.5) than as an 8 as he mostly played for Dortmund. For Dortmund he mostly was the driving force in their midfield, and I don't think it's coincidence that they bottled the league when he was injured for the final match...
Real didn't need him to play that role, not with Kroos organising the team, but they needed someone to score goals after Benzema left and he slotted right into that much different role. That's very impressive, but I don't think that I would rate the performances he showed in his Real season much higher than what he did at Dortmund. But it does give him a boost that he seemlessly integrated into the biggest club in the world. But it's just not a fluke for Bellingham, it could still be for Palmer.
I especially don't rate Bellingham's latest season higher than what he did at Dortmund because he dropped down a level in the later stages of the season (seems to be injury-related, but still that's a fact). Unlucky for England that you don't get first half of the season Bellingham, but second half.