From memory when I used to play, a shit load of skaven clanrats with slings and as many characters with fighting claws as possible (honestly so good. 2 attacks, parry, help climbing etc) seemed to dominate all.
Things have changed a bit, Skaven are good, but they struggle with leadership issues which is a huge balancer. In my experience its the player not the warband although dominant players will tend to choose between 3 or 4 warbands. For example if one of my friends chooses the Dwarf Treasure Hunters the rest of us ALWAYS gang up on him...
Also the skills were kinda unbalanced. Some like the invunrable dodge save in CC were just infinatly better than others (+1WS on the charge, +1 WS when fighting 2+ opponents, Useless!)
I'm going to get a bit nitpicky here. I realize you are dredging up bad memories whereas I have the rule book, but I don't want a misquoted rule to give the wrong impression of the game. So its actually +1 Attack plus immune to the dreaded all alone test when fighting 2+ opponents, NOT useless, usefull!
Also I have played forever and play usually one game a week so although the skill choices can become routine there are really no useless skills in the long run. Got a youngblood that always rolls skill advances never characteristic advances? +1 WS on the charge can mean the difference between needing 4+ or 5+to hit. And hitting is better than missing because at least the character has a chance.
As for randomly chosen skills over player chosen from an available skill list that is assingned to character type, the example given of the bloody minded fighter and the youngblood who runs away is exactly what happens in a game with the Mordheim rule set as opposed to the Necromunda set. Flagellent heroes are always fighters because they have no access to other skills. Middenheimer champions and youngbloods are always fighters, see above. Reiklanders are going to shoot, mostly, but Champions can become combat gods. Marienburgers have to shoot and fence because they have no access to Strength skills. (And they hide behind hired swords that they hire because they are more likely to have skills that increase income...) So if you want to do something with a warband you choose a warband with a skill set that matches what you want to do.
Finally the fact that the game is not main stream means that if you want to make it your own game you can! All the basics are there and you can fill them out as you please. There's no GT to prepare for just you and some friends. Pistol Pete has a thread going on his own house rules for his games. His Mordheim games would be different than mine, but I am going to use some of his ideas and I hope he uses some of mine sometime.
Plenty of cool concepts available for house rules though
Ain't it the truth...