It's true that it doesn't always have to be your grid, but non-grid options have their own problems. DT3 is a pretty weak multiattack buff when we're talking about characters who really want over a 50% triple attack rate to be usable, and that's locking you into playing a spear class and mainhanding a spear, which you won't always want to do. (Likewise Elysian's Call of the Abyss, which is a much stronger buff but with significant drawbacks and limitations.) Other characters also have party multiattack buffs, but that requires you to have them and bring them.Needing multi-attack doesn't necessarily mean needing grid multi-attack. It's not hard to build parties with high multi-attack buff uptime. Just having MC with Double Trouble III is 3/5 uptime already.
The point, going back to the original topic of discussion, is that there are highly regarded characters who aren't just "slot them in and they'll be good", but who depend heavily on your grid and/or party composition, and that's something for players to keep in mind when deciding who to ticket or spark. So if someone's planning on sparking a character for esports purposes rather than for love of the character, I'd encourage them to do research on the conditions under which they're fully effective, because the game is moving more and more toward requiring customized teams for specific fights rather than using a single team for everything.