Ditto what others have said, but add at least the consideration that a gerund is sometimes weaker than an alternative, even if not overused. Especially the past participial form.
Harry was running down the hall when Hermione rounded the corner and they collided.
vs.
As Harry dashed down the hall, Hermione rounded the corner and they collided.
Maybe not the best example, but I hope you get the idea that "dashed" has more punch than "was running."
Um, what you're giving us here is a "present participle" not a "gerund". It's used in a progressive construction, with a helping verb ("was") in the past tense.
Second, what you're demonstrating here has little to do with "was running" vs "dashed". You've completely recast the sentence. Compare:
1.a Harry was running down the hall when Hermione rounded the corner, and they collided.
1.b As Harry ran down the hall, Hermione rounded the corner and they collided.
2.a Harry was dashing down the hall when Hermione rounded the corner, and they collided.
2.b As Harry dashed down the hall, Hermione rounded the corner and they collided.
I'd still prefer "As Harry was dashing down the hall...", actually, because it's still the longer action that's interrupted. It's just not as obvious when you use "as", so you can get away with simple past tense. (Notice that didn't say: "Harry dashed down the hall when Hermione rounded the corner." There's a reason for that.)
The use of the past participial gerund is a carryover from our everyday speech and street talk. It's the background noise in our heads as we formulate action for a scene, and often it's the first thing our fingers blurt out. This could be one source of the "evil" gerund of which you speak.
Well, yes and no. We're using this in everyday speech because it's an integral part of English grammar, and this particular rule ("get rid of
was running" in favour of "ran/dashed/whatever") has ruined many a good sentence before my eyes. (And, as I said, it's just the progressive/continuous tense, not a "past participial gerund".)