Oh, this is apparently axed at chapter 20. I guess it all makes sense now, the author is trying to hurry to the ending he didn't set up, but that doesn't really explain why he decided to switch to different characters. He could have just kept using the MC and hurried through the training in a chapter or 2 and then used the remaining time for the tournament arc with the MC. As it is now, there are 3 chapters left for the MC to make an appearance, and he's wasted 3 chapters entirely on shit that doesn't actually matter to the story.
I guess I'll keep reading to the end since I've already gotten this far, but it would have just been dropped if this continued for much longer.