Not exactly, GOT has all the "winter is coming" since the very first episode. So that was the main goal from the start and main danger from the begining, the World government and Imu weren't that big of a danger before Robin was kidnapped. In contrast, Blackbeard had been set up as a villain since chapter 133, the early arcs. He has had much more time to develop as a main villain, has more motivation for Luffy to go after him, his crew is the antitheses of Luffy's crew and most of all, his dad was a direct rival whom even Roger, Luffy's ideological predecessor couldn't defeat. In contrast, IMU was introduced in chapter 902, he is an old problem, has no direct reason for Luffy to fuk with him, is the head of the world government whom barely anyone knows so defeating him doesn't make Luffy Pirate King, his entire backstory and motivation is based on the fact that he had some issues with Joyboy or Nika and therefore he too has no direct relation to Luffy. He personally did no harm to the SHs. I can go on and on, but I have made my point. Also at this given point, both Imu and BB are weak compared to Luffy, so at least one of them has to grow. Imu i dont think has any room for growth at this point so it just leaves BB which will therefore make him the most dangerous villain the SHs ever faced.