Discovery's release method had been part of the plan since day one, built into the fabric of its business model. Its not a surprise to CBS that is going on their upstart streaming service, that was the whole point. Along with the Good Fight, they're aiming to use franchises with proven audiences to drive subscriptions. Now, whether or not I think there is room in the market for small streaming services is a different matter. I personally think CBS would have been better going all in in a deal with Netflix to stream their content. But that's not what they've done. Discovery isn't competing on Netflix (in the US) nor in the broadcast market.
Yeah, while it would have definitely been easier for Americans and Canadians if they had gone with Netflix, CBS has long-term plans to go global with CAA, starting with Canada and Australia in 2018.
This is a great article about the business decision, and how CBS is positioned well for streaming:
http://www.hollywoodreporter.com/live-feed/can-cbs-change-streaming-game-star-trek-discovery-1037576
"It's not going to be sufficient to say, 'I only do streaming,' or 'I only do broadcasting,' " says Michael Morris, a media and entertainment analyst at Guggenheim Securities. "You want to be a pay TV network and an ad-supported streaming business."
CBS' most important move might have been its 10-year-old decision to not join rivals ABC, Fox and NBC in their Hulu joint venture. "CBS made the conscious decision to control their content and to do so in a way that left them with a tremendous amount of optionality," says Evan Shapiro, former head of NBC's short-lived comedy OTT service Seeso, who calls the upcoming Star Trek rollout "just fucking genius."