The really tricky part (as a fellow S1 vet), is that assassins were never really intended to exist in the game.
They more became a class through demand and entertainment market pressures.
A history lesson.
Seriously, look at the "assassins" that use to exist before season ~3 (idr exactly when riot started to recognize them in an official way), they were all things like "fighters" or "mages". They didn't really exist as they do now. Then people started playing extremely high risk, high reward styles by stacking pure offensive items and then using their skill, or just editing together montages, to completely negate the fact that they were dancing past instant death the whole time.
Riot said "hey people seem to be entertained by this, we should create this kind of play style for the normal player" and so the mobile AD mage Asssassin was born. Now don't get me wrong, the first few iterations of this (from my memory) were OP due mostly to mechanical undervaluing by riot, but their damage wasn't particularly spectacular, because riot tried to maintain the damage division (**abilities **scale with **ability **power and auto **attacks **scale with **attack **damage. simple i know). But what they found was that a champion like
was completely worthless if you couldn't use his innate mechanical advantage as a crutch. Yet this was painfully obvious and people fucking HATED these first attempts, because they were blatantly unfair, but also impossible to balance because mechanics are expensive to change for balancing, and the only realistic method of nerfing them through damage, set to low enough to be balanced, then you just end up back at a fighter rather than the assassin fantasy.
So instead they started to let AD creep into the role of the ability power. Suddenly you could have extremely squishy champions which could be both highly mobile and have excessively high burst damage. The 3 champions that really kicked off this trend were
, because news flash Diana was sold as an assassin first and fighter second on her release, but she was kind of that bridge of "assassins are just mobile burst".
There was one small problem that riot over looked with these new blurring of the lines and attempts to appeal to this "I'm OP and unstoppable all out offensive machine of carnage" called the "assassin fantasy"... OTHER CHAMPIONS USE THESE STATS.
The result was basically that all of the old fighters started to get OP, so they overcompensated the tanks, which lead to a tank meta. Then they said "well that's not really fair so let's buff ADCs". Now the ADCs were doing too much damage to everyone (including assassins) which really kinda fucking hurt the whole "unstoppable death machine" vibe they were going for (oh yeah and slow bruisers now juggernauts were complaining). Then they said, you know that's a little bit too much again so we should probably try to bring assassins back into the fray, but then tanks found that their defensive stats were meaningless when the assassins also had auto attacks (what are now call skirmishers) which were now designed to completely obliterate tanks on account of the ADC buffs. Then after a few rounds of that they said "fuck, we forgot about the slow fighter types", then we saw the juggernaut update. Then it became FoTY, which classes were getting "reworks global buffs", and everyone just kinda expected them to start dominating the meta again, then by the time we got around to tanks rito was like "well shit these are actually a really bad idea, but we're kinda committed now (sry supports)".
Simply put, the existence of assassins has been the cancer that spread across this game and created the arms race of damage centered gameplay. All of this could've been alleviated if they'd just introduced a 3rd primary stat (they're throwing true damage around a lot now, that could've been a decent way to balance assassins, low scaling high CD burst damage + mobility). But now they've bitten off more they can chew and been hemorrhaging players. (I literally called this exact cause like 4 years ago if they didn't hit the breaks).
All the while mages are sitting here like
[zombie-brand-facepalm]: "Tanks don't die. Assassins still kill us instantly. Marksmen clear faster and deal more reliable damage."
[cass-cry] : "Can we please get some decent itemization?"
[leblanc-funny]: "Ha, i'm an assassin now mother fuckers!... wait what?"
[sg-ahri-1]: "Who the fuck thought this >>
<< was a good idea?! Do any of the devs even play the mages?"
Probably missed somethings, this was all from memory, but the shifts in meta were kinda position based for some time during this while the arms race was just allowed to continue. What I call the "era of lee sin".