Rumblood, there's something you don't get (or even two)
Once again you compare throwing to archery which, de facto, make your points mostly invalid.
While with archery you can just stand away from melee pewpew 30 arrows or 60 if you dont take a decent melee weapon and just run when ever things get out of controle, throwing is something complelty different.
A pure thrower will more likely take throwing lances, you get four (and playing this class is actually causing me to get raped by upkeep...). You have to use them wisely, no foolish throwing, no throwing to this random cav passing a mile from you, no throwing towards this lonely archer, no throwing on shielders(even though it does pretty good damage to the shield you'v pretty much wasted 25% of your potential), when your team get pushed backwards, the missed lance throws lands behind enemy lines and there's no getting them back immediatly in the best case scenario (or just hope there's a pure thrower on the enemy team that will kindly throw them back over, but if that's zlisch there's more chance he keeps my masterwork stuff).
All this to say you have to be really selective on your targets : tincans maulers blocking a stairway (Gnjus), an old hag swinging her sword wildly (Leshma) or cav thinking your an easy target and try to couch you (my favorite!)
So, yea, let's say youv just spammed your stuff to enemy, what now? there's still 4 minuts in the battle and you'r empty handed, at best you find some throwing weapons on the floor, you'r more likely fall on heavy throwing axes, jarids if you'r lucky...
(and then next round kicks in the super awesome bug where you spawn with 3 javelins, 3 heavy throwing axes, 8 darts and a throwing lances! Huzzah!)
or you pick up a weapon in the battlefield and that's what's going to happen most of the time (because i can assure you, you'll never find enough throwing stuff on the floor to fill up your slots)
Throwing is no long distance range, you have to get up close and personnal if you wish to hit anything, and things get pretty dirty, quite often, very soon. there's no safe distance pew pewing, and there's absolutly no advantage in doing it.
There kicks in another fact, i believe, IMHO, that it is uttterly retarded to go pure pure thrower. you'll be in combat far more then archers will be, archers will be pew pewing far form the melee and running when needed(running is good when you still have ammo left...), having melee perks in their build is not necessary. With throwing it is, you have to get some powerstrike in (i have 4) and wpf (90) in order to survive, in polearms, because throwing lances do a really decent polearm, because the melee will very likely catch you up