Tutorial on Understanding What Elo is Most Affected by Targeted Changes
Disclaimer; this is not an infallible list, but if you apply it to your games, it'll help you make more accurate guesses on what specific elo will be most affected by targeted changes.
It's worth noting that there are some pretty big differences in macro play between high and low elos. This will be important for knowing how to address changes in the future.
In low elo, you'll often see -long, drawn out laning phases with little roaming -very aggressive ganks -fights taken without ultimate abilities, particularly if one person feels extremely fed -slower gold/exp gain -lots of solo fights and skirmishes, few teamfights
In high elo, you see -very short lane phases with lots of roaming. Mid is expected to show up in the jungle after 2 waves -calculated ganks, with lots of emphasis on CC -extremely aggressive laneplay if ultimates are up -quicker gold/exp gain -significantly fewer solo fights. Almost always either a jungler involved or a botlaner made a mistake so it usually becomes a skirmish. Many more teamfights, although it's still pretty lacking in this meta.
Damage Changes "Spam" Ability - Odds are, your spam ability is the one you're maxing. It's crucial to your pressure in all forms. It's important dps, it's important burst. It's waveclear, poke, etc. Damage changes to the spam ability generally affect every elo roughly the same because it's the most important ability in your kit.
Basic Abilities - When I say basic abilities, I mean every ability beside your spam ability. If you're playing Ziggs, your spam ability would be your Q and your basic abilities would be your W and E. Damage changes to these are generally meant to be more volatile to low elo. That's because there are a lot more 1v1s and fewer full fights, any loss of damage to your character is a lot more noticeable since every point of damage matters. In high elo, your second and third skills are generally utility spells so whatever damage they use is mostly negligible as you're just using the skills to enable your team to tack on damage (who cares if you lost 40 damage off Ziggs W if it allows you to throw your target into the team that can deal 3000-4000 damage to the target).
Ultimate Abilities - These mostly are for all ins and teamfights. These changes will affect the elo that teamfights more. In this meta, it's high elo.
Cooldown Changes Spam Ability - This is also a buff that favors every elo. More waveclear. More DPS. I will give a slight edge to high elo since they favor DPS over burst.
Basic Abilities - This one is heavily dependent on the skill's effect. If the skill is used almost primarily for damage/all in potential, it will be much better for low elo. If the skill is a mobility or CC skill, the changes will be stronger in high elo.
Ultimate Abilities - High Elo. You can't really be aggressive and go for plays without your ultimate. If you're a jungler, you shouldn't be counterjungling/prepared to fight the opponent if you don't have your ultimate. If you're a midlaner, you play safe and avoid assassins till yours is up. As soon as it's up, you roam. That extra 10-30 seconds can be the difference between a full minion wave.
Mana Changes Spam Ability - This one is dependent on the champion but generally affects all elos. If it's a champion that needs blue buff, it's probably more impactful to high elo.
Basic Abilities - Low elo almost exclusively. You rarely throw out these spells just to throw them out so losing 10 mana off the cost is only detrimental when you're spamming them. Think Ahri. Low elo players are more likely to fish with Charm, while high elo players hold it until they can hit.
Ultimate Abilities - These changes haven't happened since roughly season 5 when they normalized ultimate costs.
CC Changes Spam Ability - Both. High elos hit their CC particularly well while landing one or two makes landing multiple spells more consistent for both elos. Although, there aren't a lot of spam abilities that CC, and most of the time they're mainly skirmishing tools (Ekko Q) instead of teamfight tools.
Basic Abilities - High elo. Like I said, if you teamfight more packing more CC is a big deal. Makes it easier to chain CC, hit abilities, etc.
Ultimate Abilities - High elo. Again you're going for those wombo combo crazy fights that low elo doesn't really get involved with in this meta.
Range Changes This one is a bit weird since these changes don't happen often. This usually has a very strong impact on the champion depending on what skills are affected on how they synergize with the champion's kit. The most recent range changes I've seen are Lee Sin Q and Viktor W. Since Lee Sin's Q is the set up for the rest of his kit, it's pretty huge. It helps secure a lot of things he might not normally get. Viktor's W wasn't as impactful, although it does feel nice since the full gravity field will go over a wall now and not simply most of the field. I can't really gauge how it'll affect all elos but since it's being slapped on more complicated and difficult champions, it's safe to assume they're gearing these changes to high elo players.
Base Stat Changes High Elo players in 9/10 cases. With high elo players, you generally get vague estimations of how close you are to killing a target. Getting 6 more HP/lvl could change that and allow them to survive. Getting 3 more armor means you can tank quite a few more minion hits if you get too aggro. I know 3 AD is an old meme but removing or adding 3 AD to a champion's base stats is huge. In low elo, people don't utilize autoattacks as much but in high elo you generally want to weave them in as much as you can between skills. The difference between a good and bad Jax can be seen based on whether they WQ onto their target or Q auto W. AD also scales with many of these champions' abilities so over the course of a full 30 minute game they're probably pumping out up to 10k more damage, 3-4k of that going to champions.
tl;dr I divided it up into neat categories so you can look at how specific changes work. Don't ask me for an actual tl;dr