The speed of DC Fast Charging varies significantly across different vehicles based on many different factors:
1. Size of the battery
2. State of Charge (how full the battery already is)
3. Temperature of the battery
4. Vehicle battery management system programming (how comfortable is the vehicle manufacturer with charging at high rates)
5. Max power capability of vehicle (many can only do 50kW max, as of 2021)
A charger may be capable of charging at 50kW or 160kW, but very often the vehicle presents limitations, and the charger has to abide with what the vehicle wants from it. If you are seeing a slow charge, 9 times out of 10, it is because the vehicle is only requesting a particular power level due to one or more of the 4 factors above.
Articles:
1. How temperature affects DC Fast Charging Speed: https://eepower.com/news/quantifying-the-negative-impact-of-charging-evs-in-cold-temperatures/#