Not that weird. The Sheikah are vastly underused compared to the Gorons, Zoras, Rito, and Gerudo in many ways. It doesn't help that they're barely different from Hylians beyond the simple fact they wear different clothes. They don't have different skintones, there's barely any to talk about as is(beyond Impa), and Sheik feels like a representation of them alone despite her only existing to specifically reference the idea due to being trained by Impa.
They should actually give them a lot more lore, and that'd be very neat if they used a younger Impa to do so. They could also reuse her Oracles design to help differentiate the race itself. Another factor is Impa, unlike the other races, has tons of different body shapes, implying that there is no specific body design for a Sheikah. This could be why Sheik is a magical transformation, as transformations/body shifting could be a real Sheikah racial trait(and would be really neat to do). I mean, sure, they have some magical lore, with some darkness abilities implied in OOT, the ability to manipulate time and get the truth out of people(the Mask of Truth uses the Sheikah Symbol). But they still don't delve enough into it for it to matter.
Besides, every single Champion are of severely unique races that could be applied as a fighter. And you might notice BOTW is akin to Zelda 1, where Impa is an elderly lady in the story. It feels like a remake of the game in many ways, so keeping the lore similar works.