The sad part is Bellingham can become a bench player next season.
Look at Tchouameni. He was bought for 80 million Euros and he has been on the bench for Madrid and is even planning on leaving during this transfer window. There are tones of young players that have been highly rated like that but didn't have anything to show for it. A few even won the best young player of the year award.
Monaco even had a balon d'or clause to Martial's deal when they sold him to Manchester United because he was that good. So predicting that a 19 year old player going to Madrid would be among the best midfielders in the world for the next 10+ years is reaching. Very few players go to Madrid at such a young age and turn out to be the best in their position.
Sometimes there are bad transfers (even seemingly reliable ones like Hazard's transfer), but this does not mean that transfers should not be made or that one should think about the worst option. I'm glad that Real bought Bellingham and I think he will do well - he has chosen the right team. Real Madrid are ready to spend 400m and even with spending on Bellingham and (potentially) Kane there is still 200m "unallocated". Much will depend on how they are spent. But now I already have optimism about the next season.