One instance where Qui-Gon and Obi-Wan use superspeed and they never do it again. Obi might have been able to save Qui-Gon's life if he used that speed to get to him and Maul. There's far more instances of them needing to block it.
And besides, the radius of Megatron's blast is bigger than the Jedi themselves. Even trying to dodge they'd get hit.
I'm sorry, wut?
Children, children, I don't always agree with Quan, ok, BUT, in this instance, I have to say that Megatron is being incredibly underrated here.
We are talking about a mech that has literally millions of years of wartime experience, with includes a vast repitoir of close combat fighting styles. Megs was a gladiator champion prior to forming the Decepticons. Outside of this, he is also packing a variable yield fusion canon that has, more than once, crumbled mountainsides... You stick him in a room with 3 organic beings, and he fired it, the squishy fleshies are going to be splatter juice even if they could get to the other side of him due to the concussion wave alone...
I mean, what the ever living hell....