You really think Blizzard would let the game in this state for months without adding content ?
That would be a quick way of losing the interest of most of your customers. The game needs more content.
I mean, we know Blizzard is excellent about content generation. Let's look at their history.
World of Warcraft's last patch was...June 2015!
Diablo's last patch was April 2016, that's better! The one before that was January...
StarCraft 2 fares pretty well, with patches in May and March most recently.
At best, that's two to three months between content. Now, Overwatch is their new game, I'm sure they've got people working on it as fast as possible. End of June was quoted for Ranked returning, I'm sure we'll see at least something around then. But let's not kid ourselves that Blizzard has a good track record with this.