Then again the size of guidance systems have shunk a lot in the last ten hears.Any warhead or kill capability will be based on the ARRWs target set which would have been defined by the USAF quite early on (when they put the T in TBG). That would also impact guidance and other trades.
It is now possible to make a quad mode seeker the size of a cellphone these days, looking at the GDU53s. Hell the Army has a tiny GPS guidance kit in the PGK. And batteries have come an extremely long way too.
Either way, it will not surprise me if the Arrw has a sizeable warhead thanks to the guidance being tiny.