I think MK is overrated, he's not as bad as he used to be at one point in the metagame. Development has stopped moving as fast so I think other characters will have an opportunity to catch up to some degree.
Here's a basic rundown of how MK's go down:
Bad player = ok metaknight
Pretty goodplayer = will beat your secondary
GOOD player = You need to use all your notes for this one.
It's not that hard, it just requires the extra mile of effort! Besides if anyone wants to get decent at brawl you would be walking that extra mile anyway, finding what you need to in the MK matchup along the way.
I think people like Ally and MikeHAZE have the ONE special trait that people refuse to use:
Creativity!
Come up with weird punishes to MK's cookie cutter approaches. Ally Dairs tornado if they finish on him and Mike counters drill rush offstage.
I think the lack of creativity is what's holding a lot of people back vs MK.
IMHO.