The LVCC Loop started boring in 15 November 2020 and opened to the public on 15 April 2021 - so 5 months, for the 2.7km. The Channel tunnel began construction in June of 1988 and opened for freight trains in June of 1994, so 72 months for the 50.4km.

So, the LVCC was built at 0.54 km/month, while the Channel tunnel was buildlt at 0.7 km/month.

Which part is false?

Isn’t it expected that a longer tunnel would take less time to build per mile than a shorter one? That just seems obvious. Just like how a 2000 square foot house isn’t going to take twice as long to build as a 1000 square foot house.

Not really - especially when that longer tunnel is an international project and is being drilled under the sea, not a straight line in a desert.

Now calculate km per month per dollar.

I didn't say anything about cost in my initial post. Still, you're right that the cost difference is hugely in favor of the LVCC tunnel if we only look at length.

However, if we look at freight+people crossing the tunnels, the Channel tunnel surely wins again - it may be roughly 10 times more expensive per km, but it carries orders of magnitudes more, by rail + by car.