I see some problems here: one could make a cleric/monk (which is a VERY strong build at 20s) and stick it to lvl 20/25 using the lvl remover to kill any toon of the opposite faction infinite times... also, they could kill the same target over and over again simply by waiting the 10 min rule cap.
As for leaving certain builds at certain lvls...it isnt illegal and some builds are better at lower lvls...some at higher. If somebody wants to spend the rest of the year playing one toon all the time not farming and sitting around waiting for pvp more power to them. Course they will prob get bored and quit anyways. killing same target over and over again...for an entire year???????? the guy dying is probably going to avoid that pvp battle after his 1500 time dying or so :/ If it was a week or even a month i might agree with you but over 12 months i have to think that this wont be an issue. We havent had same bounty hunter 2 months in a row ( i beleive) yet....