If you fuse with someone your stats should be added and not be multiplied by 2.
And if you are a namekian you can learn a little bit diffrent Fusion. If you fuse with a namekian the Fusion is permanently. Something like picollo did with nail and kami.
No he’s right Metamoran Fusion adds up technically speaking. But since the warriors are supposed to be equal it’s like multiplying by 2. And Namekians’Absorb and Fusion are 2 different thing that do not give the same scale of power up.