Where did the idea of magical girls being ultra-violent battle-happy beamspammers come from? This is distinct from merely being inclined to fight first and Zettai Daijoubu later; to qualify, the magical girl in question has to have their abilities occasionally defined in terms of "blast radius" and "ground zero".
The obvious source that comes to mind is Magical Girl Lyrical Nanoha, but like all obvious sources, it feels a little too obvious. I'd accept Nanoha as having popularized the concept into the mainstream, but I'm interested, in an academically-fascinated kind of way, if there was something earlier.
Despite my love of the genre, I don't actually know a lot about the history of magical girls. My interest can be traced quite directly from Card Captor Sakura (the best anime of all time, OF ALL TIME), and then expanding silently and insidiously to other examples of the concept, such as Minky Momo and Akazukin Chacha and suchlike. I suspect there may be an element of wish-fulfilment in these shows for their target audience: wouldn't you want to be someone with Special Powers just for a while? And since anything in life that comes free is viewed with perhaps justified suspicion, the price is having to keep it secret, or having to fight against the forces of darkness. Good, clean motivations, without much moral ambiguity.
Gigantic energy beams of annihilation might fall under the Special Powers category, but I'm not sure if they're as clear-cut in wish-fulfilment. This seems to be more or less the domain of action-adventure stories, particularly since these beams do damage; a lot of "classic" magical girl deals with "purification", rather than "beating the stupid out of". Here is an Enemy: would you rather use your powers to make them a Friend, or to blast them into the bedrock?
(Yes, I know Nanoha and others of her stripe tend to do both at once.)
Interestingly, apart from Nanoha herself, I haven't seen many straight examples of the beamspammer magical girl, and certainly none that come to mind right away. Most of the examples I've seen are one-off parodies in other anime, which focus both on the damage potential of the character of the show-in-a-show, as well as the fanservice and its effects on fandom demographics. The male late-teens to early-twenties anime fan is a frequent target of derision, particularly if they're seen to be interested in a show that is meant for a "purer" class, like the actual preteen girls the shows were originally said to be for.
Which makes it all the more stranger when the show is deliberately aimed towards these male anime fans, often to the direct detriment of the preteen girl demographic, and yet makes fun of its fans. Maybe we are assumed to be able to take a joke.