You might be right. I think Cobra works because we don't actually have cobras here. So it sounds dangerous and exotic, but safely distant. The last time I ran across a live dinosaur? Again, dangerous and exotic and safely distant. Besides, when I hear "raptor" I picture birds. Tremor? I grew up in earthquake country and all that reminds me of is a stupid movie. And jello. Lighting? Why would I fear lighting? Is it as scary as indoor plumbing? LOL Lightning is rare and generally not feared because it's usually viewed from inside shelter. I've been caught out in it a few times and it scared me. The name still works for me because the first association in my mind is that it's effing fast. And as a force of nature, it's in a different category than an animal, especially an animal that many consider vermin. School mascot is a whole different category of product and I don't see how it applies.
It's also weak from the sound perspective. Good names have a minimum of one hard consonant in them. Raptor has one. Cobra has two. Rattler has none and turns to mush in my mouth.
No matter what name you choose, some people will hate it and some will love it. It's a percentage game and you want a name that lots of people like and few dislike. With not one, but two strong negative connotations and a weak sound, I think Rattler is a poor choice. An obvious poor choice. Your liking it is just fine. Lots of other people will also like it. But that doesn't make it a smart play. I'd put it on a par with Asp, another dangerous snake that's safely exotic and has a hard consonant in it. Maybe that's their next model name.