So you're telling me that Obito had 3 eyes then? He'd have used the only eye he had left for that. Which means no space-time dojutsu for him.
Also, remember that old maxim, "Just because I've taught you everything you know, doesn't mean I've taught you everything I know?" Minato probably never had reason to show them Hiraishin level 2 (probably never had reason to, due to how feared he was and it seeming like more of a one-on-one technique). Remember, Naruto didn't really know anything about Senjutsu until Fukusaku told him, not Jiraiya.
(Not that I think it's Obito or anything...)
Izanagi resets all injuries the only thing that changes is the eye closing. We've seen it against Konan and Danzo against Sas. All they do is imagine themselves back to safety and they're there. Danzo was recovering from Sasuke completely destroying his entire body. Why would Obito recovering an eye be ridiculous?
That old maxim was proven wrong multiple times in this series. None of the students have been surprised when their teachers break out their big gun techniques. They go on S ranked missions together so it's not like they're ever gonna hold back. Not only that the other ninjas in the village are aware of everyone's techniques. It's not a competition within the village like it is outside.