To say he popularized something all these guys already did is to absolutely say their efforts weren't noted, only Em's. Now you're backpedaling. MCs are influenced by multiple people, of them all types of names pop up. I'm sure you listen extra hard when a guy mentions Em and overlook all the NWAs, Pacs, B.I.G.s, even Canibus references when someone speaks on their influences. I'm not going to try to statistically establish foundation off the net where vids can be posted multiple times to alter number of views, and things like people who sit in front of a computer vs people who play Cds or whatever can change results. I guess PSY popularized muting the beat as a transition into the chorus and nothing before him mattered because Gangnam Style was such a big song? I'm not saying Em isn't bigger than Pac, I'm saying 75million people heard Pac. 100 Million heard Em. If anything we can just stick to those numbers and say 25 Million were late hearing adlibs(still not even saying pac was 1st to do it, but you heard adlibs and were aware of the technique before 1999 if you were into rap, period). I could even break down why that's still not accurate because those were sold on albums over a period of time that Pac started a decade before Em and all but sold as consistantly as Em did on a Cd to CD basis, but forget it, I'm wasting brain cells.
Point is, you said Em "popularized" a mixing/performance technique that has existed as long as multi tracking and existed in rap since day 1. THAT IS ABSOLUTELY FALSE.
To end on a positive...Eminem did popularize shock rap, even though guys like Skull Duggery, Brotha Lynch, TechN9ne, Gravediggaz, Raw Breed, Redman & Cam'ron existed before him doing the same style, none made it "popular" to rap about crazy things like raping dogs, worshipping satan, and killing wives. He also popularized white rappers even with Vanilla Ice, Beastie Boys, Milk, Remedy, Lil Whyte, White Dawg, H.O.P./Everlast, Snow, and others existing before him, and some leaving huge marks. The reason i still say he did so, was because milestones like Vanilla Ice hadn't made a record in a decade when he came out, and Everlast and the Beastie Boyz had moved into Rock/fusion genres so they weren't categorized the same at Em's arrival. He popularized diss records, even with them existing since the beginning of hip hop, because of his shots at N'Sync, Britney, Xtina and other heard across the world, it became popular for rappers to directly name people when talking shyt on a more mainstream scale. Long gone were the days of KRS/Shan beefs that only made noise thru project hallways. Em is very influential on hip hop culture, but has nothing to do with popularizing a structural technique even Michael Jackson used. "Hee hee/Sha'mon!!!".