Comparing on a percentage point basis, you have to ensure that the underlying physical system is equivalent, in this case, the capacity of the batteries.

Current superchargers charge at 2% / minute. I am assuming that's the maximum rate of charge, given the current supercharger infrastructure.

Lets assume that 2% / min is, say, at a 100 kW power level.

When charging a truck, assuming the supercharger technology isn't changed, the charging will still be at 100 kW power level.

So if the truck has 10 times the battery capacity, then the equivalent %age rate of charge will be 0.2%, not the same 2% as the capacity of the battery to be charged has changed.

Personally I think Elon is either going to add multiple charging inputs per truck and combine it with a special supercharger, or have some sort of port in the truck to which a special connector is connected to transfer huge amounts of power safely, not unlike a dock at the under side of the truck, or maybe the front.