Why British and American carrier losses had different effects

Were British carrier losses in 1940 as dangerous as the US Navy's losses in 1942?

No; Britain retained more geographic and infrastructure advantages, while Axis fleets still had to pass the Royal Navy to reach the Atlantic.

The Royal Navy retained alternative infrastructure even after its carrier losses in 1940. Its German and Italian opponents also had to pass British-controlled exits before major units could reach the Atlantic. Geography and sea control therefore preserved British operational options despite the losses. The US Navy's rapid carrier attrition in the Pacific created a different crisis because carrier availability directly constrained reach across the theatre.