It's the usual thing too of the Earth-2 characters being a bit more "primal." In the same way as their Superman was simpler and tougher, their villains were VERY nasty and pretty basic about their drives. Some have a misperception that Earth-2 was more innocent. Oh fuck no. That was pre-Code--it's Silver age they're thinking of. These guys were bad news.
I mean, the U-H has to murder people and animals just to live, for one.
Point is, Brainwave's behavior here is totally in keeping with his character and makes sense in context. And is fucking evil.