In finance, if you’re long and short the same asset it’s considered risk neutral.  Now one could argue these are not that same asset, and we agree... Our base case is that lightning will never be worth LESS than on-chain.  While on-chain can be worth less than lightning. 

 I hear you but you are violating the KISS rule.
Something that would be more interesting would be arbitraging Bitcoin in different exchanges/countries.
Maybe it will work out - but not for me 

 ah like the south korea arb