Every MMO has this annoyance .. WOW has stuns, LOTRO has cripples, etc. .. seems MMO devs just like being annoying whenever they can.
First hit should give you heavy, the second hit should throw you down the chocobo and the 5th hit should kill you if you don't kill the attacker first.
It made a lot more sense when there were pockets of extremely dangerous mobs all over and especially around the far aetherytes. Kind of an added "you're screwed" chance while making your death runs to attune to them all. These days though, getting drive-by heavy is merely "Seriously. Seriously? Ok, I'm going to get off this chocobo, turn around, and then kill and eat your entire family." Annoying and pointless.
I don't fear death in this game because...
Even if it WAS really easy to die, there really aren't any consequences.
You don't lose exp. Durability is super cheap to repair, and oddly... you don't lose THAT much durability from dying.
And with the 'closeness' of aetherytes, it's not like one death will waste 30+ minutes of your time.
Compare this to FFXI where if you died in the 'open world', you would beg your friend to come out and raise you because...
1) You could lose hours-worth of exp from 'homepointing'.
2) You would lose 15-30+ minutes of progress because you would have to run that distance again.
But... a 'you lose exp and a lot of money from dying' model would make the game less convenient for casual players who simply don't have the time to play. Thus... you are right. Heavy is a minor inconvenience, because death is not really an inconvenience at all. Plus, the mobs don't hit that hard so heavy REALLY won't kill you fast anyway.