And I think the reason, this time, is that the episode didn't spend the entire time trying to convince the viewer just how clever it thinks itself, it just told the story and the story was lovely.
That's because overcomplicated and clever are different things. This story was not clever. It was a lot of arbitrary things happening quickly.
I mean Villengard could've just rented the dinosaur room and left the briefcase there, they didn't need to mind-control anyone!
Yep. I cannot imagine someone at Villengard saying, okay, here's the plan, nice and simple, nothing can go wrong. We need a power source, right? So we're going to put a star in a briefcase that controls the mind of the person carrying it and makes them creepily say something weird and ominous so that people around them know something weird is going on, and if they give the briefcase to someone else they die and the next person goes through the same experience, and since we're in a time-active era the most easy and straightforward way to send it to the past is to go to a time hotel and get it to the ancient past of a planet whose history is extremely significant to the development of this whole galaxy. We'll have our star --- of which there are literally billions already around here -- at the cost of changing all of recorded history. Anyone have any concerns or questions?
Meanwhile, the Doctor needs a password and a future Doctor shows up, tells him the password and that he has to take the long path -- not, it turns out, to get the password, but to give himself a lesson he's already learned repeatedly over his various incarnations.
But he was going to get a new companion anyway, he wasn't that broken up and he didn't need to wait on Earth. The Doctor always comes back from leaving a companion behind, he just broods about it for a bit sometimes. Ruby isn't Rose (well she kind of is in that she's a bland young blonde woman, but you know what I mean) or Amy or Clara, The Doctor didn't need to learn some lesson to "get over" her.
And if he does need a companion, Anita is right there. If she's sufficiently unimportant to her time and place that she can be recruited by the Time Hotel at the Doctor's suggestion, she's also free to travel with the Doctor without changing history.