Noisy Rhysling said:
That doesn't make them "smarter", I think, just more adept at innovating. I don't remember any instance where a wizard came up with a "new" spell in the HPverse.
Sectumsempra (had to google for the spelling) was invented by snape as a child, it's the non-verbal spell that slices someone up. Also the Weasley Twins develop all sorts of magical items that they go onto sell in their shop, IIRC some of them were objects that maintained protection spells around the wearer and they were so good the Ministry ordered hundreds.
I'd say that this, plus a few other instances (explicit and implied) show that the wizard world also researches and innovates new magic. Different to muggles sure, but in the HPverse there's a whole extra set of physical laws (magic) that can seemingly only be manipulated by specific people (wizards)
Noisy Rhysling said:
But yeah, the wizards didn't seem to have any weapons of mass destruction. They would have had to fight a guerrilla war, and those are usually long, hard, and costly.
True, except the wizards have a few huge advantages:
1) They already have experience hiding in muggle society (admittedly it may become harder if they are actively hunted)
2) A number of their spells make point 1) easier, like hiding a house between two others on a street or casting a spell that makes muggles want to leave when they enter an area
3) Their offensive magic is extremely capable on a close-quarters setting. A well trained wizard could likely block incoming fire from weapons, disarm multiple opponents, pull them out of cover, mind control/stun/kill them etcetera.
4) Their regular magic would be extremely capable at circumventing muggle military/security doctrine. Specifically they'd make excellent assassins. Pretty much every wizard can teleport virtually anywhere in the world, they also have access to invisibility cloaks. No political or military leader would be safe from a wizard invisibly popping into existence in their bunker and killing them (or placing them under mind control).