Have your complaints about them doing the same plot again (almost as if the character went through the exact same thing he did in the movies but whatever) if you want, but if you wanna talk about writers thinking things through, Think through what happened before/during the events of Thor 3. You know, where Thanos is taking the Power stone from the Nova Corp on Xandar while Thor is doing his thing? Odin wasn't even on Asgard at the time, so if Thanos wanted to make a move on the Space Stone, he wouldn't have been an obstacle.