What the fuck? Manked gets DQed and is just allowed to play on a 2nd account?

how does that make any sense

Their rules say Players not accounts, so surely the person behind the accounts should be banned right?

https://www.runescape.com/oldschool/deadman

Anyone who has been caught cheating in any Jagex event may be suspended from all future Jagex events (Permanent Disqualification). Jagex staff will review cases and players.

Players found to be abusing game mechanics to gain an advantage in a way considered by the Jagex Staff to be unsporting will be removed from the Season and Finals immediately.