She's saying that Samurai and Black Mage have to interact with mechanics more so than Machinist and as a result, they should do more damage as they have to try harder by that metric. Technically this is also true of Red Mage as RDM has to interact with mechanics differently as a Melee DPS or a Caster but it taxes the DPS it should be given by having access to Verraise and Embolden. Black Mage is only justfiably stronger than RDM because of it's utility, both have very high levels of optimization when it comes to fight design. The community has just been fed a myth that BLMs have to be super good to do mechanics and keep dps and RDM aren't trying nearly as hard to do the same thing. They're really even in difficulty or close enough that it's subjective but for different reasons.