There is no question that a short hitter can be a single digit index. I also think that the longer you hit it, the higher the ceiling on how good you can become.
Even on tour, the very dominating players have almost always been long, relative to their competition. Jack was. Tiger was. Dustin Johnson is today. Brooks Koepka is. The list goes on. Yes, there are exceptions. Lee Trevino was not considered to be long. Nor was Gary Player. However, generally speaking, as others have said, distance translates into greater potential.
One of my regular golf buddies averages only about 195 yards off the tee and he's using a hybrid or FW from 145 yards or more. He's a 9 index because he putts and chips it well and his misses are very small. He really struggles to play to his index if he plays any tees over about 6450 yards but will often break 80 if you put him at 6200 yards. If he could play my average drive of 265 he'd be a 5 index or better. On the flip side, my son and one of his buddies finally took an interest in golf now that they are almost out of college and won't have the time to practice much, lol. They both are much, much longer than me but they both score in the 90's or 100's most of the time. Hitting a golf ball far and crooked more often than not is not a unique skill nor very helpful for breaking 80.