Nope. that's when they refer to the Yonko as the 'greatest' pirates. Strongest speaks to combat strength.
and Stephen's script:
"
Garp: Among the countless masses of pirates in the world,
he is one of the four greatest, along with the infamous Whitebeard,
"
If it meant political power then Viz would have used greatest here like Stephen who works for Viz used in the Garp statement, but they didn't