I'm not the biggest fan of a lot of Em's newer stuff, but he had some quality tracks on this new album, like The Ringer.
Also, I'm fairly certain that Em didn't just dig up the issue with his daughter from 6 years ago. I read that MGK took some (small?) shots at Em on a track with Tech N9ne, which seems strange to me, since Tech worked with Em on Speedom, which was a huge song for Tech, and he's said he really respects Em), so this was Em just getting a little dig back at him in a song/album where he goes at a bunch of people.
The thing about Em, that even people who don't like his new stuff will admit, is that even if he lacks the same appeal and unique creativity, the same authenticity as he used to have, he still has some technical rap skills that are elite level; way above the technical abilities of MGK. I recently heard multiple people say that if rap was an Olympic sport, Eminem would still be a gold medalist due to his ability to spit and rhyme, but the actual content of his tracks may not be what it once was. That said, we'll see what he comes up with next, as he's been a historically good diss-track rapper, and maybe he just needed a real reason to get back into it and come out with a solid return to form. MGK's rap at Em may have had a few good digs in it, but it was certainly not technically elite/great. We know Em's response will be technically great, and if he can go back in time and pull out some lyrics/disses like he used to have, it'll be a slaughter.
Also, regarding the whole "hungry vs full" thing, remember what Arnold said:
"The wolf climbing the hill is hungrier than the wolf on the top the hill."
Arnold: "yeah, but if the wolf wants the food, it's there"
Em hasn't had a real reason to want it, but maybe now he does.