Sizing of different PCB polygons on different layers for high current
You used a tool for calculating track width for current. As far as i can judge, the tool is made to calculate how wide a track has to be for support a current of a certain amperage. This is for tracks that only transport current, think of it like a cable. Usually the large polygons are not only for the current transport itself, the also serve as a heat spreader to take heat away from the device.
You can use this Calculator to find out appropriate values for your parts