Funny thing with discussions like this is that you're not necessarily taking the production skill into account. You're considering how highly regarded the rappers that made songs on said production are now when they were in a completely different era.
So, of course, you're going to get a bunch of people saying Premier's better because he did songs in a more lyrical-focused era on albums with an upcoming Nas and Jay-Z. He's 49 and it was different then. Only the classics will be considered in this discussion and folks will gloss over all the disposable shyt (Afu-Ra, lots of Gangstarr shyt that people DON'T know)
Metro Boomin's only 22 and the artists he works with are thriving in an era where party music is the wave. Shouldn't diminish the fact that he actually has skills and it shouldn't be ridiculous to say that he can eventually be held in high regard. Same goes for London On The Track and Mike Will (who I think is brilliant, and could actually make this discussion more interesting).
Carry on though. I expect to see a lot of "Metro Boomin' could never make a "Nas Is Like" or a "A Million & One Questions". I'd be willing to bet that the same would be done with a Timbaland or Pharrell or DJ Dahi. There's a bias against modern/party music when discussing greatness.