Is removing a players progress for a long period of time necessary for one game of flaming?
The only time this happens is if the player is using hate speech or encouraging self-harm, in which case they get an immediate 14-day ban.
In normal cases a player goes through a 10-game chat restriction, a 25-game chat restriction, and a 14-day ban before losing their account, and sufficient good behavior can lower or reset the progression.
For a player to be permanently banned, that player needs to have receive their warnings and then not sufficiently reformed their behavior. After three warnings, it seems reasonable to take more decisive action.
If a player has another account who has become friendly and honored alot, shouldnt their other account be lifted onto a lesser punishment like a month or 2 weeks?
No. The permanent ban is Riot's indication that they do not think you (a proverbial you -- not aimed at the OP) are well behaved enough to be part of their community. They are aware that they cannot STOP you from making a new account, but they do not want to offer incentive to do so -- they would rather you find another game to play.