Number tweaks can mean different things based on champion / context.

A lot of people like to joke about certain changes, that seem stupid, negligible, when they are quite impactful. Of course, there are changes that are indeed stupid and negligible.

Let's start with an example. Zoe's Q was nerfed by 0.25 seconds a while ago. That was indeed a STUPID CHANGE. It did nothing and everyone knows it and everyone memes about it.

Now, let's talk about the Janna nerf, that reduced her base MS by 5 and her W damage by 5. People seem to think it's a stupid change, but it is quite impactful. And the reason is because there are certain things that need to be taken into consideration before assuming things. Janna is a champion that is heavily reliant on her MS. She has a lot of MS boosts but has no mobility, so she needs as much MS as she can get to engage/poke in lane and run away when she has to. Nerfing her base MS by something as small as 5 can mean that, in some situations, certain champions can outrun her attempt to engage a poking sequence, or that she can't outrun them after she used her W. Also, her AA and W damage are also scaling with her bonus MS, and her W grants bonus MS based on her base MS. Pair that with the -5 damage on her W, it can potential mean a damage reduction of 10 damage when going for a W-AA combo at level 1, for example. It might not seem enough, if it's just one trade, but if she can do that 3 times during level 1, that's already 30 damage taken away. That's also another 30 damage at level 2, and so on.

Assuming you agree, or at least attempt to understand why such a change was quite impactful, and actually showed in her win rate dropping by 1.6% over patch, I want to talk about a change to Graves that's coming on the next patch. The change is that Graves loses a flat 3 AD and also his R CD is decreased by 10 seconds at rank 1, 5 seconds at rank 2 and stays the same at rank 3.

Now, people believe it's a stupid change. A "lol 3 AD" change, or a "lol 10 seconds" change. But it's not stupid, it's not trivial. It's actually quite a big deal, because of how Graves works in the jungle.

The 3 lost AD can mean that a camp takes one extra AA to clear, which means like 1 extra second needed to kill it. If he has to reload, it's like 2 seconds. If that happens for every camp, it can mean a potential loss of 6-7 seconds in tempo, where the enemy jungler can contest a Scuttle Crab, or steal a camp without you being able to stop them, or denying you the potential of counterjungling yourself. I have played quite a lot of Graves this season over 3 accounts (more than 200 games) and I can confidently say that his timings and tempo will be slightly slowed down and that can be quite impactful.

Also, to the R CD change. There are two types of champions; those that want to spam R off CD, because of the impact, and those who don't. Graves is one of the champions who want to spam it off CD whenever possible and generally want to have it as a safety net. Similar champions are Malzahar, Skarner, Warwick, Malphite, whereas the other type of champions include Soraka, Zac, Jax. These champions don't rely on their ultimate to do a good play and only use it to enhance what's already there. Therefore, back to Graves, having the cooldown increased by 10 seconds can potentially mean that an invade is not safe because his R won't be back on and might dissuade him from actually trying to do it.

TL;DR: Graves' changes will be quite impactful. I can't tell for sure if his win rate will drop, because of new items coming in that will definitely impact him as well, but it would, if the items wouldn't come in.