In the FFXIV world, lore-wise which job is the strongest if there was a tourney?

[The_Last_Dragoon]

the NPC in the Stormblood Black Mage quests would destroy Estinien.

Beware, black mage quest spoilers ahead!

I get the feeling that you're associating the Shantotto in FFXIV with the Shantotto in the FFXI universe. The Shantotto from that quest line is not only a mere echo of the person who actually created Black magic was, but once again they play second fiddle to the Warrior of Light. Not to mention that there is very little to be shown that accurately gauges exactly how much power Lalai has while fused with Shantotto. I would also deign to point out that the whole fact that Lalai is only powerful because she's fused with Shantotto is made very evident in the quest line (which means she's powerful because of something other than her job) and it's to the point where Lalai is actually limiting the power that Shantotto has. Estinien on the other hand is strong because he's a Dragoon, period.