Look at how fast Griffin can jump here, you are seriously underestimating his powers.
YouTube video
In particular:
:40, he jumps from the desert to Tokyo in the bat of an eye.
From 1:00 to 1:19, he is jumping the car here and there, onto the sides of buildings, as if it were nothing.
2:09 to 2:17, he is all over the Coliseum, it takes him like a millisecond to jump.
2:39, he jumps the truck at Rice Bowl.
BTW, I totally forgot he can jump in midair, from one spot to the next, as shown in the vid, he and Rice Bowl can. Not to mention he jumped an entire bus at Sam.
So, he ports onto a Decepticon, ports it away, then is back in maybe two seconds. The Decepticons will be on the move, no doubt, but they will be in the same general area. So when he returns, he ports to a vantage point a few hundred feet away, waits for the right time, then ports another Decepticon away.
And if Starscream or Megatron take to the air, he can simply port onto them, then port them into a volcano.