I think for a lot of people, Eminem is their "Baby's First Hip-Hopper" and then his influence gets overstated, and yeah, there's a racial component to it of course because a lot of these same folk were ignoring non-white lyrical rappers before them or they didn't get exposed to those artists because of racist radio.
But I think because he did come out of the gate lyrical, it did pave the way for a more mainstream acceptance/awareness of lyrical rap, and in terms of that more mainstream lane, sure, Em is significant. But rappers were doing it before him, kept doing it, and are still doing it, and significant names have been doing it from jump.
Maybe it took a white dude to get racist America to be more ok with it, and that's impactful yes. Maybe The Roots/Black Thought never get to be the band for the Tonight Show, for example. But Black Thought was doing his thing before the Tonight Show and Em and been doing it, of course.
But as time passes, I don't think Em's peak output (while great to me, let me say for the record) will be considered extra significant by hip-hop historians when it comes to breaking ground musically compared to other eras. Like, it won't be or (shouldn't be, anyway) considered similarly to the coming of Rakim or Illmatic, for example.
Not saying it ain't worthy of some recognition, but lyrically game changing, nah, not like that. Em was just another part of that branch that extended from Rakim but who propelled to mega success for obvious reasons on top of his supreme skill.
And to Em's credit, he shouts out his peers and precursors who are supremely talented themselves and who, all things being equal, deserve more recognition then they get, like say, Pharoahe Monch.