Why was louis xvi considered ineffectual ?

 Well, for one... Louis the XVI was considerd ineffectual because he was usually depicted as rather a weak sort of king. Not really able to wield the strong centralized state in which his ancestors had crafted.
 *And he was also seen as an honest man, who had good intensions, but who was most likely unfit for the strong task of reforming the monarchy; He basically wasnt the best man for the job... 
~Therefore, He was ineffectual, just like the question states...

~Hope this helped! Anymore questions, please feel free to ask. :)