most hardforks I seen the newer coin crashes then people buy it back when it dumps then it recovers and the old coin crashes

right?
ETH/ETC as an illustration, both BTC/BCC will coexist. I wouldn't compare to other shitcoins.
Better arbitrage maybe buy either coin on weakness and sell on strength.
Remember Ethereum Classic is old blockchain Ethereum fork from incident The DAO ICO in 2016. For avoid attack from hacker, Ethereum decision HardFork their blockchain to two part are Ethereum (New) and Ethereum Classic (old blockchain hacked). So, it very different Bitcoin (Core) and Bitcoin Cash in current!