Final Fantasy VII literally includes this tier system that you're trying to say doesn't exist - it uses it for Chocobo racing (no idea if remake does, I've been avoiding spoilers about it). Several other FF games include systems which use the F to S ranking system - FFIX and FFXV for example (the MMOs also do, but that's kind of a given).
Re: RPG tiers - nope, they haven't "always been" colour-coded. It's easy to prove, given the original 3.XE tier list was numerical (note this is a repost of a repost of something from the WotC forums, I forget when it was originally posted, but at least a couple of years before that).
Tier System For Classes (Repost)
web.archive.org
I don't know when colours came in, but I first started seeing it in 4E. They're dominant in situations where you're ranking a very large number of things, because you don't have to put a letter or number next to something, or group under a letter or number, you can just write naturally and colourize stuff to quickly indicate value. That's a different approach - you don't normally rank things like entire classes that way.
I mean, that list is definitely very incomplete and the sudden burst of games using "s rank" in 1998/1999 is likely a result of the list being impacted by the fact that most of the people adding to it are of a certain age (early-mid 30s and younger). You can see this with GiantBomb lists in general - despite a lot of the writers being a little older, any game that came out in the later PSX era or after that is vastly more likely to be on a list than stuff from the SNES/Megadrive era. Also for whatever reason, stuff that came out on Nintendo consoles is vastly more likely to be covered, as is stuff that came out in the US. You can see they missed out FFVII, I note, perhaps that's because it's from a minigame, but it's more likely they just didn't know. But they also missed out FFIX, FFXIV and FFXV, where it's not as obscure. So I imagine they're missing most games which use it.
But I agree with the general timeline. Whilst I think we could probably dig up some games from before 1993 if we systematically went through SNES/Megadrive (maybe even NES/Sega Master System), and we could almost certainly dig out a lot more in the mid-1990s, it's clear that the system of F to S rank became more popular over the 1990s, before becoming very popular in the very late '90s and beyond. At this point, if you play any kind of retro-indie game that's emulating the style of 1990s-era games it's reasonably likely to use F to S ranks - Streets of Rage 4, for example (even though SoR 1/2/3 didn't have it AFAIK).