You could probably say that for a number of final fantasies honestly.
In FF8, the only playable character(s) that actually mattered was Squall and arguably Laguna. The other characters are just there especially after disk 2.
In FF7, honestly, all the playable characters besides Cloud and Aeris fall flat as far as the main story goes (which considering those two were initially conceived as being the hero and heroine of the game this is not too surprising). I'd probably rate Tifa as coming in 3rd.
In FF10, Kimari, Lulu, and Wakka really don't matter. Not exactly sure whether to lump Rikku though she certainly adds little overall beyond wanting to prevent Yuna from fulfilling her journey. Even Auron's significance to the overall plot is very limited.