Honestly, this just feels like a really cynical commentary about the community (which I think you should dial back because it's peeking out), because those two words... literally do have meaning, provided someone can back them up.
If I said right now, "just have Dark Mind boost your healing gained by some percent and it'll be fine," your response would be that DRK doesn't have enough self-healing to justify that change in direction. That's a discussion about whether things have value within or even directly interfere with other elements of a kit. If I said synergy was "just a buzzword" in just a response I'd be laughed out of the thread.
Likewise, if I said right now, "I have to weave 3 different cooldowns for DRK to get the same protection and sustained survival that a PLD can get just tapping Holy Sheltron," there's a discussion of reward versus gameplay depth and skill ceiling that should be had.
As for "weight", if a skill has a hitstop effect and a flashy animation but still only doles out 150-200p damage (coughAssassinatecough), there's a problem with the actual potency of the effect not justifying its visual performance.
More commonly though, I see this being used when discussing abilities that are culminations of long periods of sustained attack, particularly back when SMN had a two minute rotation just to get to Bahamut back in Stormblood.
