6 4 or even 2,5 and 2bb bet size shouldn't be related to "only" JJ it should be related to table dynamics, to opponent habits to position etc... If you get called by trash hands when you are in position why don't you bet a bit bigger, or you have multiple callers why don't you bet bigger... but dont size it according to your hand, that is a big no no...
Players overestimate a lot of hands, how else would you explain 60 70vpip, same post as above can be posted if we are talking about AK, Ax suited or not, small pockets, any suited cards etc... You can't say that JJ is a weak hand, you cant say that it doesnt have showdown value, of course that you have to be able to let it go if needed but heck there is times when you'll let go aces to if not, you are in troubles m8, but if you are long enough at the table or have enough info on players or have good notes and found leaks or patterns in their play ill say that JJ can be really profitable hand