First of all - and this is with no disrespect to you, but - exaggerate, much? For real, blowing Riot's policies out of proportion, and equating the permaban to "merciless murdering". No offense, but it's hard to take your post seriously when it seems so...Campy.
Second; if the player in question played enough games to regain Honor 5, I have a hard time believing he didn't de-escalate to a clean slate on his account from a 14-day ban. IIRC, the rough estimate of how long it should take to de-escalate a tier is 6~ months worth of consistent, sportsmanlike play, so if he spent a year and a half behaving, he should've been on the 10-game CR tier at the very least.
Ultimately meaning, if he broke the zero-tolerance policy the first time, netting the 14-day ban, and at least de-escalated to a 10-game CR, he'd have to have broken the zero-tolerance policy again for him to be straight-up permanently banned.
And this is all assuming that your story about the guy is even true - you don't provide any links, so as far as we know, it's all just hearsay or made-up to try and preach about how "needlessly harsh" the system is.
Players already de-escalate the punishment tiers through consistent sportsmanlike play, and it doesn't need to be tied to Honor progression, and here's one good reason why;
If Punishment tier decay was tied directly to the Honor system (meaning Honor Levels would be representative of a tier de-escalation), people would use that as a way to game the system and be consistently toxic without having to worry about losing their account, because they'd know "okay, I climbed back up to Honor 2 or whatever, now I can tell people to fuck off again", and afterwards "okay, now I'm Dishonorable again, so now I gotta wait a while before I'm free to be toxic again".
The goal of veiling the de-escalation in obscurity and giving no information about it is so that players don't decide they're in the clear and able to be toxic again - they shouldn't be toxic, and if they know there's a point where their account is treated as though they never had a penalty at all, they're going to try and abuse that so they can be toxic.