Game of Thrones was good for a few seasons, but half way through the fans started dropping almost as quickly as main characters. DC movies have had very few genuine successes, even if they've technically turned a profit.
Putting all that content up on Netflix would be unlikely to pull in that many more subscriptions, and would require dropping the existing streaming service(s) and agreements to allow for exclusivity.
This doesn't bring significant talent or IP to Netflix, it's just an attempt to grab market share. I doubt they'll try to move anything out of WB/HBO's existing streaming platforms or agreements. This just looks like an attempt to increase profits by simply buying a profitable company and letting them mostly continue to function with minimal changes.
In other word, this probably isn't the worst acquisition possible for consumers, but it certainly won't improve life for anyone to let it happen, and it does consolidate market share and control when it comes to media. This probably won't be hugely evil, but it won't be good either.