Amateurs...

In some games it is genuinely unplayable. This is coming from someone with on average 200+ ping with spikes up to 600 sometimes.

I guess I don't really play any games where that tiny difference in ping time matters THAT much...That's less time than most people can even measure without tools
- Would matter in pretty much any game where one player's actions can affect the other player and position is important.
  SA:MP back in the day had such shit netcode you had to shoot a significant distance ahead of a running player or nothing would happen to them. It was the shot receicing player's client that had to detect the shot. In games where the server determines what happened to you, 100ms means there's 100 milliseconds where you don't even know you're dead. That said, unless you're playing competitive, 100ms is still borderline okay. Near 200 it's horrible already.
  Now something like a game of Civ? You could have an entire second and be OK.

If the person shooting you has 30ms ping, I'd say it's a significant advantage.

To human perception a 0.1 seconds isn't much different than 0.03 seconds
I forgot if it was you I asked about this or not. But are you sure the one with slightly less ping time isn't just cheating?
if a person shooting me has a lower ping and I get upset about it with a 100 ping I need to touch grass.
back in my day I played Halo with a 1300-2000 ping and still whipped ass.
- I don't believe you. An fps with ping as massive as over 1000 would be straight up unplayable
  That's over a full second of delay! In an fps I routinely do split second maneuvers and reactions. If someone I was shooting at wouldn't be able to react to what I was doing for at least a full second, I would easily dominate them every single time
  
  believe it or not. this was early 2000s, so everyone outside of major cities had shitty internet.
  I had the fastest connection in my small shit town at 1.5mbps.
  
  I also don't believe you, and here's why:
  Halo CE didn't have lag compensation, so with 2 seconds of latency you would have to lead your target by 2 seconds. Shooting anyone who wasn't standing still would be a complete guessing game - I think you too would also classify that as unplayable (source).
  Halo 2 seems to not be well documented - it looks like it's using some form of rudimentary rollback, which can deal with higher latency but you'd need it very stable to avoid opponents teleporting constantly. It's also unclear if it would handle 2s of latency, as that would increase both CPU and memory utilization of servers. If you're getting a variance of 700ms as you claimed this most certainly wouldn't be playable. High ping being stable is also hard to believe, naturally the higher the latency the higher the absolute variance.
  Halo 3 uses synchronous lockstep networking with a ~300ms window (source). If you're not in that window your actions are rejected, so quite literally unplayable at 2s. I think this is more evidence that bungie would've had a <2s maximum latency in their earlier title.
  My best guess is you've either misremembered the latency (130-200ms is about what I'd expect from rural internet at that time), or you were playing peer-to-peer with your friends and so internet latency didn't matter. I myself have played plenty of multiplayer games at over 100 ping and while it can be annoying I'd certainly call it playable, but not 10x that.
  
  I don't always get 1.5mbps now and 1000ping doesn't work in a shooter. Depends on the game, some will make you basically unable to move, sometimes you basically warp around visually and fuck all happens, sometimes it seems fine but you die to people that don't exist because you have a second of delay.
  I was dealing with spikes of 2000 to 10000 ping yesterday on Minecraft and playable is not a word I would use to describe those spikes.
  
  thresholds today and thresholds 20 years ago are vastly different.
  my point was that it's possible to play a game even at "high" ping.
- the lama's ass?

I think over 100 starts making your off-gcds clip on FFXIV, and stuff like getting 6 hits properly for Wildfire on MCH(probably some other stuff too). It's not unplayable, but it is frustrating and distracting, so can cause an ADHD person like me significant stress when doing content like Savage raids and Ultimates

Final Fantasy 14? Don't know what MCH is, never heard of Wildfire
- Mch stands for Machinist, a ranged gun class in FF14, and wildfire is an attack from said class that gets stronger the more hits you land during its duration. The max hits is 6, but enough lag and you can only get 5 of them off in the window. The game has a default 2.5 second global cool down between skills, though some gear and some skills can reduce that. In particular for Wildfire, you combine it with a skill that allows 5 hits of itself plus 1 other at 1.5s per cool down, but if you're adding another .1 to each of those it can add up to miss unless very tight on timing.
  Not a game breaker, but if you're trying to push through your best performance because your group is failing at 1-2% you can't really help not being mad at it.
  Edit: in addition, the frustration isn't you personally dying in some pvp, but your group of 8 friends you're also holding back on fights. In addition to lowering damage, deaths can wear down your healers mp(and significantly lower your own damage output) so some tight mechanics can be harder to react, especially if your brain has you move wrong at first. None of these by themselves are terrible, but over the course of 3 hours working at clearing multiple fights it can wear you out and kill your enjoyment.
  
  Edit: in addition, the frustration isn’t you personally dying in some pvp, but your group of 8 friends you’re also holding back on fights. In addition to lowering damage, deaths can wear down your healers mp(and significantly lower your own damage output) so some tight mechanics can be harder to react, especially if your brain has you move wrong at first. None of these by themselves are terrible, but over the course of 3 hours working at clearing multiple fights it can wear you out and kill your enjoyment.
  I don't even do PVP in anything anymore. It's too stressful to be the only one who's trying to win while the other team is a group of friends that are full of gear I can't get. Between that and the people who actually cheat to win, I just can't do it anymore.
  How do I know they cheat? because my attacks registered with a pretty high amount of damage and their health didn't go down even one bit. Other times, the same attacks with the same character will wipe out each enemy player I attack and it requires the entire other team to focus on just me for me to die
  I like to play as stealth classes and I'm good at going to places most people don't check, you should see how I play Gmod prop hunt. I'm great at it

As an amateur, in a fast paced shooter, vs. an equally skilled player, it went from a fair match with equal pings to one player dominating the other with 100 vs. 70 ping.

that little of a difference really matters? Are you sure that the one with a tiny bit less ping isn't just cheating?