The difference between this years Derby fractions and those of other years (War Emblem's Derby win excepted) is that the horses setting the early fractions in prior Derbies all caved in the stretch (lots of lick but no stick ), while this years front runners never tired.
It's probably too early to compare Smarty to the great horses of the past, much less Seattle Slew. The Derby win was impressive but... the track favored speed horses that day. His previous wins did not come at premier tracks against top-notch company.
I suspect he will fare well in the Preakness - probably win - but the Belmont 3 weeks later? We'll see.