I think Kawhi and Ross are much different players. KAwhi is undoubtedly a better defender (he's elite), Ross is above average at this point. However, they are pretty equal as far as offensive impact is concerned and Ross has more potential to grow.
Since Casey has been giving Ross more minutes after the ASG (23 games, small sample but still enough to matter for a sophomore), his TS% is .590 - Kawhi is .597. Considering half of Kawhi's shots come off cuts and slashes that are a product of Pop's system. Also Ross attempts 7(!!!) 3s a game and shoots them at a 41% clip.
In summary, both really good role players who do different things offensively. Kawhi with the advantage defensively and Ross the higher ceiling.