Tyre mileage

I know the above is tongue in cheek but sub <30k wouldn't be too unusual.

I once got 58k miles out of a set of 195 65 15 firestone firehawks.

Wheels were rotated once and changed once they hit the wear mark.

Next set of firestones lasted 30k miles

They werent firehawks though

The question with your i40 OP is what does the tyre wear look like? Have you any pictures of them?

Better quality tyres will wear faster.

It's a trade balance grip/longevity, if you want a tyre to last 50,000km then buy as cheap as possible but be prepared for terrible grip.

Having worked as a mechanic and now in fleet management, I've seen people get between 5000km to 40,000km out of similar tyres, the other consideration is your own driving style, the road surfaces and road types.

20,000km is a safe average.