...I am curious why in this day and age Riot still can't develop a decent ban system for intentionally feeding in games...
Well, to start off with, detecting intent is always going to be difficult to develop a system for. Very few cases of intentional feeding are legitimately clear-cut, and an automated system will always have trouble discerning intent when there's so many factors to consider.
Beyond that, the community in general doesn't help matters much, considering how frequently people report others for underperforming, regardless of whether or not the poor performance was intentional. Or, as I like to call it, "crying 'wolf' over a pug".
...but one wrong word even with no priors ever is now 2 week ban worthy (not even chat restriction)...
If you skipped the chat restrictions from a clean slate, then that "one wrong word" must have been really egregiously wrong, because you only skip punishment tiers if you're being punished for an exceptionally awful offense, like zero-tolerance chat.
I thought the whole point of escalating bans was to create a kinda safety net in the game so you know how far along you are.
It's not a safety net, it's a punishment ladder. Increasingly severe punishments for players who belligerently refuse to follow the rules, and the tiers can be skipped (as mentioned previously) if you use zero-tolerance chat, such as hate speech or encouragements of self-harm. If you commit minor/moderate offenses, you'll doubtless climb the regular punishment tiers, but break the rules in an especially egregious fashion, and Riot will apply an equally strict punishment.
But to seriously lose 2 weeks over one chat problem in one game seems absurd...
Again; You'd have to have committed a pretty egregious offense to warrant the jump to the 14-day ban. The fact that you don't provide your chat logs or anything further than vague statements about your behavior makes me suspect that you used zero-tolerance chat, in which case, the 2-week ban is absolutely warranted.
...when you can run into feeders that do quite honestly more harm, and don't ever get banned.
They do get banned, they're just harder to catch than chat misbehavior. As mentioned before, discerning intent is extremely difficult, especially considering that the community has a habit of filing false reports against players who simply get their asses handed to them.
...someone with no priors shouldn't get a two week ban when you are on a team of four feeders.
Other people breaking the rules doesn't make it okay for you to break the rules yourself. If Riot just arbitrarily gave free passes to break the rules on account of other people breaking the rules first (or even specifically for other people "intentionally feeding", as difficult as it is already to verify), then there would be a whole host of nonsense where players start vilifying anyone who starts performing even remotely poorly, under the pretense that any feeding = intentional feeding and that means they should be allowed to flame whomever they want.
So, naturally, Riot's not going to do that. You don't get a free pass to break the rules at any point - it doesn't matter if other people broke the rules first, it doesn't matter if you can prove without a shadow of a doubt that the player you flamed was feeding, you are required to follow the rules you agreed to. Full stop.
And yes I am speaking about myself and while I do regret what I said I think a two week ban as a first punishment is insane as a first offense level punishment especially that it puts you one step from a perma ban.
Without seeing your chat logs, we've no ability to comment on your punishment. As far as we know, your punishment may well certainly be merited.
Skipping the Chat Restrictions and jumping to a 14-day ban is not unheard of, and it's only just shy of uncommon. Spewing hate speech like racial or homophobic slurs or encouraging self harm guarantee that jump to the 14-day ban, because that is behavior that Riot considers zero-tolerance - you should know better than to act that way, and Riot punishes players fittingly with that expectation.
And how long does that take to decay even? Last thing I want is this broken system to kill my account so I am curious.
From a 14-day ban down to "clean slate"? A long, long while. De-escalating a punishment tier takes around 3-6~ months of consistent play without breaking the rules, and you're sitting on 3 punishment tiers. You may as well round upwards and say you've got roughly a year of no misbehavior ahead of you if you want your account back in "clean slate" standing, and even that's far from a certain estimate.
And, no, the system isn't "broken". If you used hate speech or encouraged self-harm, the punishment of a 14-day would be appropriate.