People have many different play styles. Some people use long range rocket mortars, others use close range arcs. Its all about what playstyle suits the player. If you like the get-in get-out style, try arcs or shotguns. But some people may play it more safe and use jav racks. Honestly they are all good choices if you play them right.

Javelin rack weakness: 15m minimum range, get within it and javelin racks are rendered useless unless you can somehow smack your opponent with something else.

Killshot ability: Smacks enemies with it's face.

Killshot weakness: SQUISHY

Javelin rack strength: Hit mechs from behind cover, a lot less risk involved using it.

I don't think I need to explain it more than that. They complement each-others weaknesses nicely. Killshot as a close range assasin does still work, in fact it's a lot more rewarding if you can pull it off, but it's a lot riskier.

The  kill  shot  boost  is  a  boost  with  damage.  No  one  said  that  you  had  to  smash  people  with  it.  An  artillery  or  missile  assassin  works  with  being  able  to  zoom  out  of  the damage  zone  and  shoot  behind  shelter.

Missile  assassins  are  powerful  but  balanced.  A  control  point  capture  is  great,  as  you  can  shoot  at  far  distances  and  either  destroy  or  be  destroyed  by  other  killshots  in  either  close  or  far  range.  The  one  with  the  most  skill  for  the  particular  match  uo  will  win.

i've  been  killed  so  many  times  by  close  rangers,  so  many  from  far  rangers,  I  have  destroyed  so  many  far  rangers,  and  somany  close  rangers,  and  i  always  do  missile  racks.  

You  can  absolutely  wreck  a  more  powerfull  mech  requiring  four  clip s  or  more  by  using  the  walls,  and  you  counter  other  missile  maniacs  by  being  close  to  the  wall  and  moving  back  when  you  want  to  fire,  meaning  that  it's  a  dance,  not  a  hide  fest,  but  a  dynamic  skill  fest.  You  can  die   easilly  or  destroy  six  mechsbefore  taking  damage  and  then  blowing  up  in  a  single  shot.  

The  seeking  missiles  work  fine  for  assassin  archetype.  In  fact ,  I  hate  myself  for  that  kind  of  play  style,  but  it  still  requires  skill  to  make  it  work  because  the  mech  is  balanced  and  made  out  of  paper,  and  I  can  die  really  easily,  so  I'm  kind  of  fine.  It's  not  so  much  a  sniper  shoots  a  few  shots  and  gets  less  kills  but  less  deaths  but  a  skill  heavy  do  right  or  die  thing.  It's  notjust  do  this  and  win,  so  isn't  exactly  all  that  lame.