Why a replacement carrier is not immediately combat-ready

Did rapid American and British carrier replacement avoid any immediate loss of quality?

No, because commissioning, crew seasoning, air-group integration, and systems workup all take time.

A new carrier needs more than a completed hull before it can replace a combat loss. The ship must commission, its crew and air group must work up, and the combined system must prove that its equipment functions. Sending a newly commissioned carrier directly into battle would expose avoidable weaknesses. The answer distinguishes fleet size on paper from the number of seasoned ships actually ready for combat.