I am putting down their argument yes.
Lack of experience isn't the sole reason.
I am saying they lack experience and have also made multiple factually incorrect statements which coincides with the lack of experience.
In contrast, players who do have experience all day otherwise because they have the experience to know better and not make the aforementioned factually incorrect statements.
If one understood the differences, they wouldn't be complaining. Sure, Graves' cancel removal or Renekton's cancel can be discussed. But bringing Riven into the equation is entirely irrelevant. She has nothing to do with either.
Graves' cancel was removed because it was a bug giving additional power to an already strong champion. Riot has also acknowledged the existence of the bug personally explicitly.
Renekton's is because he could cancel his autoattacks up to three times in a row (which is even faster than Riven can cancel her AAs, she just has more canceling overall), and four times with Tiamat/Hydra. Riot deemed this was too much I'm assuming on a semi tanky champion who was already dominating earlygame.
Riven's cancels were a bug initially but were then incorporated into her kit and she was subsequently rebalanced around it because it fit the theme of her whole character better. She is in a balanced state, as evidenced by both statistics and otherwise from pro players or extremely high ELO players, and multiple other factors.
Thus, quoting Riven in the argument against removing the cancels in Graves' or Renekton's kit shows a fundamental lack of understanding of the differences.