Which one is more important for lifespan issue.
The engine, or the catalytic converter? If I may say, of course its the engine.

In US,yes, the Catatylic converter is important to pass the emissions test,
but in Malaysia, Puspakom dont give a shit about it.

That's why the newer API poses a more serious issue for older engines due to reduced zinc level., just to protect the cat, at the expense of engine life.