Look at the Steels that tran doesn't beat: excadrill, m-Metagross with Earthquake, m-zor with superpower. All but the latter still beat volcanion, and even then m-zor is 5 speed BP faster so it can potentially u-turn out. And heatran obviously hasn't broke the metagame, so why should volc? Less of a catchall typing, weakness to rocks, and lack of rocks in it's own movepool, as well as lesser special defense, probably even out the hydroscald and higher coverage.
Speaking about the actual metagame, it's gotten a lot bulkier since I last played. 100 and 110 are still big speed tiers, but the base Speed stat average hovers just above base 91. Granted, that's not factoring in EVs/natures and scarf, but still slower than you'd expect. You see a lot of slow phat shit on balance like washtom, tangrowth, tran, amoonguss, slowbro, clef, Ferro, skarm, hippo, gastro, the list goes on. This is why Hoopa is thriving, why bandtar and band terrak are gaining traction, why SD defensive landog is a thing. Wallbreakers eat that half of the meta alive. Anything slower probably can't switch in, while anything faster probably doesn't have the bulk or HP to spare to take a hit on the switch. Even offense tends to stack wallbreakers along with their standard anti-offense stuff, and runs stuff like m-zor or a defensive ground to make the job even easier for opposing wallbreakers, furthering their viability even more.