I’ve seen some people think Rune Fencer/Mystic Knight instead of Corsair, though Rune Fencer/Mystic Knight tend to be more tanky than DPS in previous FF games.
As for the t-shirt, we already have Monk, Ninja, and Samurai… so, maybe it’s reference to the turtles themselves. I’ve seen some comments suggest Green Mage since the turtles are green. There’s also the theory that since the turtles are all named after famous artist, it’ll be a job based around calligraphy and magical inks. I’m pretty sure an “ink mage” would be a first for the FF franchise, but it’s not an uncommon archetype in other Asian RPGs.