Right at the bottom of the heap, Pit-Slaves are terrible in play for several reasons:
1: They have no bullet stoppers. The cheapest gang member is 60 credits before arming him.
2: They have next to no shooting. They can take one heavy (who never gains experience), and the leader and (BS2) techno can carry special weapons. No other pit slave can shoot with anything more than a pistol. So the firepower they can put out is pathetic.
3: They don't have either agility or stealth skills. Which means they might be able to tear it up in close combat - but they have nothing to either speed them up or help them dodge bullets so getting to close combat is a problem - the same thing that makes Goliaths weak.
4: WYSIWYG and you can't change weapons around. A pit slave's Pit Slave weapon is literally attached to them. So no taking the Buzz Saw and giving it to the WS 5 Pit Slave who only had a Rock Drill.
5: No swords. There are no swords on the Pit Slave list except the single chainsaw arm. Swords help you win fights rather than just do damage. So you have trouble even winning fights in melee with Pit Slaves.
Which means that in practice Pit Slaves work out much like Goliaths (the weakest of the gangs) except with a number of disadvantages Goliaths don't suffer from like weaker heavies, no juves, and no covering fire from people with basic weapons.
My thoughts on Pit Slaves (as I'm running them in a campaign and I can't possibly comment on all of your lovely long posts):
Problem 1 assumes you need bullet stoppers - careful use of cover allows people to survive, and the extra 10 credits on top of a normal ganger is due to the extra advance they get, which if its +1 T you're getting bullet stopping power there. Also, depending on the rules Pit Slaves get armour saves from the get go very cheaply, which again is bullet stopping power.
Anthony Case's rules cover problems 2 and 4 (0-2 Technos, pit slave weapon upgrades, weapon transplants etc.) - I never understood how wanted convicts would get ahold and maintain a servitor, even if they had a techno. Even under normal rules, you're confusing firepower with range in a few cases, as Plasma Pistols are still available for decent power and damage, and arming a techno with a grenade launcher provides a more versatile "missile launcher".
Problem 3 is less about having Agility or Stealth, and more about how less accessible those skills are (I have a Pit Slave who started with Leap, lucky me) - and as far as getting into close combat, treacherous conditions or simply hugging terrain can help immensely, or are you a fan of fields of enemy fire?
Problem 5 is House Weapon Lists.
Why play them? Even if you use them, you can still rare trade item a sword and put it in their flesh hand, which if you're in close combat is the only time it would be there, otherwise it would have a pistol in it. You also seem to forget the Parry skill (the only reason a sword is considered more powerful), the chainsaw is just a chainsword available for the whole gang (leader-only weapon anywhere else but Van Saar?) and the utility of a Pit Slave Hammer (1/2 or -1 WS, depending on the rules you play).
Pistols are pretty versatile, being both ranged and close combat weapons, and certainly starting off can be a boon for high-strength hits to put someone out of action (Plasma Pistol!). It also doesn't single out particular gangers for enemies to target ("get the heavy!").
Another simple house rule that would balance Pit Slaves could be that bionic arms can replace Pit Slave weapons (its a pretty expensive measure), and combination with the Specialist skill would allow for some extra ranged firepower.
I agree with the lack of juves and heavies per se, in that I'd love to strap a buzz saw on a juve and send him out there, but its the flavour of the gang and the challenge of an Outlander Gang play style versus a House Gang - you could argue that other gangs are poor because they don't get access to S5 close combat weapons as common items from the get-go.
As a final thought, if your entire fighting force is just sitting there with long-range guys on overwatch, trying to pick enemies off as they move between bulkheads and ruins, at best you're not in the spirit of the game and you'd probably win the The Most Beardy Player Shaving Kit, and at worst you're going to get your ass handed to you as you're a sitting duck while the enemies close in around you.
If its a multiplayer game, the other players will ignore you and lay into the easier opponents (each other), let you "win" by voluntarily bottling, and come out on top in terms of experience and advances (you can't get +5 per wounding hit if you don't wound anyone, and winning usually only helps the gang leader).