Picking Royce Gracie makes it seem like there is a disconnect or misunderstanding between what MMA is or why it is popular. If UFC 1 never happened the only difference is the #1 MMA league today would have a different name and slightly different history.
Some of Royce's opponents like Shamrock and Sakuraba are more important for MMA. And no, they wouldn't have needed the Gracie storyline to become popular, MMA was already becoming a thing in Japan, the UFC had nothing to do with that. Royce is not even the most important Gracie, it's likely Rickson.
McGregor has brought MMA to its biggest commercial heights. Not unlike Jordan or Woods. No, it doesn't matter that he isn't as good at the sport as those guys are at theirs. Takeda, Lesnar, GSP, and Ronda are all responsible for large expansions for MMA's popularity, more so than Royce Gracie was. Most people don't remember or even know, but Wanderlei Silva was a way bigger deal in Japan than Royce Gracie was, even when he was fighting Sakuraba.
The UFC of today and UFC 1 are basically two different entities. MMA existed without the UFC, and existed in a couple of different countries under different names. So I don't think Royce Gracie is quite the most important person (I'm assuming this is based off him winning the first couple UFC tournaments). The UFC was rather irrelevant during Royce's time.
If Royce had not fought (or any of the Gracies), the only difference is the narrative for UFC 1 would be different, or another no-holds bar tournament would have happened instead.
The UFC and Pride definitely could push an event behind Royce Gracie, but he wasn't that useful for expanding the market to non-MMA fans, which is kind of what makes someone important. Otherwise, what are we talking about? MMA is just entertainment.