I understand that if it were to pick up speed it would get there in less time. I don't care if it is redundant. This second part of the sentence was irrelevant to my point thus I did not cite it.
My point is that when it goes in a straight line it never gains speed except when its engine is thrusting. The only way it can gain speed is by slingshot maneuvers, and in order to engage in one of them it must bend its trajectory. There is no such thing as a straight line slingshot maneuver.
What I'm trying to say is that the full statement isn't redundant. It seems redundant when read "
(allowing it to pick up more speed) and
(travel much further in the same amount of time.)", but it isn't when read "allowing it to (
pick up more speed and
travel much further) in the same amount of time.".
The first interpretation conveys the fallacy you pointed out, but the second one doesn't. It doesn't seem to be about the top speed, but the time of acceleration and total mission time (which is the topic of the article).
The first interpretation claims that going in a straight line somehow accelerates the spacecraft. The second one claims that using flybys to get to the same speed will take more time, or that it takes so much time that it's not worth the extra speed.
Since the first one's less relevant, redundant, and false, I think the latter is the intended interpretation.