I hate Modern Spongebob from Season 9B to 13.

nah…discord is the strongest creature in equesteria. all these times it was like he was playing a chess…

Honestly, I still like Discord in much the same way as I like Q from Star Trek: the Next Generation. And honestly, it makes all the sense in the world for the Spirit of Chaos to do something like this, especially when the stakes are the monarchy of Equestria. You would want the next leader to actually be able to lead through difficult times, else they might end up making mistakes that could harm many other residents of Equestria. Was this the best way to go about this test? No, of course not. Honestly, I think that might have been one of the worst ways to try and prove Twilight’s ability to lead. However, it does fit Discord almost perfectly, as it is very much in line with how he was introduced all the way back in S2.  
Also, for the record, I think that Grogar was originally meant to be an original character, and the writers changed that later on to possibly add yet another twist to the story before the show ends. And it seems to have worked