2. And yes. In 1953, Bassey signed her first professional contract, to sing in the touring variety show
Memories of Jolson, a musical based on the life of
Al Jolson. I guarantee there were other applicants for that job.
....and she was deemed the best applicant, so she got the job. If there was no immigration at all and this was a pure white Anglo-Saxon country, the best candidate would STILL get the job, and there would still be people with shattered dreams and ambitions.
And thus she DID "hold back native talent".
Thus there is a negligible benefit to the UK, in that Bassey was slightly better than the next to best singer,
while the cost is that one "native talent" UK citizen was denied that opportunity.
If you want to show a benefit to the UK from immigration, you have to show something good that happened to the UK, that could NOT have happened without immigration.
Showing a good singer who happens to be a child off an immigrant does NOT do that.
The UK would still have had excellent singers without immigration.