Just to add on about ELO:
ELO rating system is a method for calculating the relative skill levels of players in competitor-versus-competitor games.
A player's ELO rating is represented by a number which increases or decreases depending on the outcome of matches between players.
After every game, the winning player takes points from the losing one.
The difference between the ratings of the winner and loser determines the total number of points gained or lost after a game.
In a series of games between a high-rated player and a low-rated player, the high-rated player is expected to score more wins.
If the high-rated player wins, then only a few rating points will be taken from the low-rated player. However, if the lower rated player scores an upset win, many rating points will be transferred.
In certain games after reaching a set amount of ELO a player gets the chance to rank up, in SLO this would be the jonin exams.
TL;DR: So basically ELO is a rating system, technically speaking people with a higher amount of ELO should have a higher chance of winning against someone with a low amount of ELO but they won't get as much out of it.
The system is fine, as it will be individual ELO instead of group ELO.
You will get or lose points depending on how much difference was in your ELO and the opponents ELO.
Regarding noob sniping or whatever, there's hardly any way to counter that.
Low level people shouldn't be in dangerous zones to begin with, so it is their fault if they end up dying.
If people go rogue before getting Jonin it's their fault if they can't get better jutsus though.
that's a consequence they'll have to deal with if that system gets implemented.
Edit:
You don't have to be a village nin to get ELO, a rogue ninja can also get ELO by defeating opponents.
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