Sure, they didn't know music history so well ("there's three of us but we're not the Beatles"?! Of course, John Lennon was dead by this time...) They might have smack talked a whole lot of sucker MCs. They might have gone through two needles on every jam they played.
But Run DMC were hip hop pioneers - the first consistent hitmakers of the genre - the first to bring actual instruments and not just turntables into their music - the first to popularize adidas - the first to use Larry "Bud" Melman in a music video - and with good reason. Run - Joseph Simmons - and DMC - Darryl McDaniels - played off each others' rhymes with seamless ease. And they had a fair amount of anger in their music, too. Hip hop before Run DMC was happy, and talking about how they were the best MCs, and dancing. Until Run DMC started calling out sucker MCs.