I don't think there's enough playtime on Jhin to really come to conclusions (he's not even released yet; Yes, I've played him on PBE and have some sense of his style, but there are going to be a lot of new things people figure out when he's released; I mostly played him in 1v1s, so I don't really know how he interacts in teamfights)
This being said, I don't think he overshadows her. Yes, Jhin feels more like a sniper than Caitlyn, but Caitlyn isn't really a sniper. If we're talking military, Caitlyn's more of a rifle(wo)man, where yes she has long range, but also a lot more versatility and consistent damage, where Jhin focuses more on preparation and very impactful single shots from long range, like an actual sniper. If we're talking theme/fantasy, Caitlyn's a sheriff, not a sniper. She uses a rifle, which is why she has long range, and she's a sharp-shooter/has good aim, but that doesn't mean she's a sniper. A sniper lies in wait for their target and takes them out with precise, high powered shots; they're basically an assassin that works from super long range. This is arguably why Xerath is classified as an assassin secondary.
They have some similarities in their kit as far as range and traps and such, but I think there will be enough differences in how they play that there isn't that much overlap. Caitlyn is a solid ADC in almost any circumstance; Jhin feels much more specialized and will have significant strengths as well as weaknesses. With Jhin, especially if you want to maximize his range, you're going to need at least one other consistant damage source on your team; Caitlyn isn't exactly a hypercarry, but she is much better at being a consistent damage source than Jhin. I think Caitlyn (if played properly) will still have much more lane presence than Jhin because of the consistent damage and the long AA range (also better waveclear).
