While it doesn't allow invalid transactions, it does enable rolling back other people's transactions, by a combination of rolling back time and rejecting a class of transactions, such as a particular address. In particular, it allows ignoring all other miners and taking all the newly mined coins.

It's true that the further back in time you want to rewind, the more computational resources. In particular, the further back in time you want to go, the more time it takes to accomplish the maneuver. But if you are a consortium of miners, you were going to spend these resources mining, and the total number of blocks is fixed, so does it cost electricity? I'm not sure.