I dunno if you still check this but... I have a couple "friends" who tell me that I must play a certain race and clan to get the most out of my class and that I'm not good if I don't do that. Is that a true thing or are they just trying to make me play a race they like?

I don't check it as much as I should.
Race matters very little in Stormblood. The stat differences between races are very small when compared to the benefits you gain from gear now that ilevels are high.
In realm reborn, race mattered. In heavensward, it helped early on. In stormblood, you won't notice.