I think Stormblood actually had a mostly slow as hell pace for combat, get a load of the first boss of the first dungeon, Eminence EX, or the first raid boss (Alte Roite, both versions). Even savage endbosses were largely categorized in the now commonplace "mechanics soup puzzle every 1-2 minutes with a couple different versions throughout the fight, much downtime between," StB was the first to do that.

When people attribute to StB good combat, I think they remember the increased spectacle attained from leaving behind the PS3 and pushing for memorable moments like the big sword in Susano, the transition in Byakko, o4s or climbing on Shinryu. Creative mechanics like Worker-8's mathematics I feel weren't really unique to Stormblood though; they've always pushed the envelope on surprising mechanics, even if they weren't executed in a memorable way.

What it did have over Dawntrail was more job complexity, only coming down from the peak of punishing job design in HW, sometimes even forcing unnecessary gauges into jobs so that they could each have a unique UI element, sometimes changing their design trajectory. But the job design being diverse and more involved I think in turn made the combat experience more "complete" feeling, despite the slower pace of encounters themselves when compared to HW or DT.