When converting Lion hulls into carriers makes sense

Could Lion-class ships have been converted into aircraft carriers?

They could, but conversion is chiefly an emergency expedient; a purpose-built carrier is often the better answer.

Converting a Lion hull would be an expedient for a crisis in which carrier capacity was desperately needed and neither new hulls nor building space were available. In the scenario discussed, Britain could already produce enough carriers for its own needs. The apparent early production gap followed a policy decision to pause capital-ship and carrier construction rather than an industrial inability to build them. This watch point separates an emergency conversion from the stronger long-term case for a purpose-designed carrier.