A disclaimer:
I'm not saying that samurais aren't powerful characters. They are: they roll huge buckets of dice for shooting, punching and slashing. Second, this doesn't involve so much character concept, as much usefulness of the archetype, because, damn, a Sammy can be cool. In this sense some builds may vary, a hacking sammy that can do other stuff in a proficient way may break the argument I'm doing here, so I'll try to stick to the classic role in the party for these characters. That role being muscle.
Many of these arguments can /also/ be extrapolated to the Physads. This is true, however I decided to keep them still since their initiation and ability to perceive in astral, and the possibility to build wards sets them apart, for now. If you ask me I'd rather have mystic adepts than full blown physads in a team.
A) The Deffinition of Street Samurai:
These are characters that use cyberware or bioware as primary for their combat skills. They are the riflemen in a group, the demolitions experts and martial artists. They are part tank and part damage dealer in MMORPG terminology. They can stop a Panther Assault Cannon round with their chest and come out of it alive thanks to armour layering, dermal sheaths, bone lacings, etc. These characters are a classic in the Cyperpunk theme, and may very well be the roughest, toughest, meanest killing machine on the streets.
Now, the question of a million

My argument will try to deny this.
B) Sammy Skillset (SR4):
A proficient sammy knows: Firearms (or subsets), Close Combat (when was the last time you saw a sammy take: Incompetent Unarmed Combat, or Blades for that matter?), Stealth, Etiquette and Athletics. That's a minimum to consider one viable to be added to a team. Demolition guys, medics and tech-savvy ones may be a bonus, but not the rule.
C) Why we don't want a player to roll a Sammy (from a team efficiency point of view)?:
The past subset of skills can easily be covered in other ways by other characters who have additional talents. This is the main argument.
Let's start with the obvious one: firearms and Close-Combat.
C.1) Rifleman and Knife-man:
Sammies shoot very nicely, so you want one on your team. They also take damage, instead of squishy mage. Drones can do this, and even more efficiently. They don't need patching up, can be reapired if the team has someone with mechanics and can be optimised much cheaper than the cyberware a Street Sam carries. For sensors you can add and mix and share information from lots of little robots. On the other hand if your Steel Lynx is shot beyond repairs you don't go al guilt ridden for stripping it of base components and sell them to a junkyard. A Sammy is a pal, an alive team member who also needs to be taken care of -like squishy mage-. In a pinch I'd rather have the dornes do more shooting instead of the Sammy if just to make sure my friend doens't get hurt.
Close combat is a tricky one, but a summoned spirit can usually do the trick. Also an Adept or mystic adept, that can initiate and get nifty powers during play, can replace the sammy. Yes, they will not have all the dice the sammy has, and they may, at the start, be less powerful than him. But each can outgrow by far the sammy for practical reasons. The adept can support astrally with perception and a weapon focus, and can also carve enemy martial artists. For a gunbunny adept there is pure win, since they can combine magic and shooting for huge exploding dice. The mystic adept has some minor sorcery and conjuring to aid in his "Close Combatiness", and after a while, with functional spells this guy supports a lot the group (he has utility spells like analyze device, detect enemies, Detect RFID tag and Wreck RFID tag, for a magical tag eraser which does take care of stealth and reinforced RFID's). He can also initiate, and get nifty metamagic.
The Combat Hacker does a lot the sammy can do, add some skillwires and he's also incredibly versatile. Just see how the Lieutenants on mook groups are hackers /and/ warriors (SR4, BBB, pp.275 and 276). Same, and even better, is the combat technomancer, who uses agents and sprites to support the other team members, has a nigh unhackable brain -except by other virtuakinetics- and can go through submersion.
The Rigger -or Drone and vehicle hacker- can do a lot of the aforementioned, plus scouting, driving, all of this keeping at a safe distance form harm. He's an artillerist, air support and get-away pal rolled into one. Again, his drones make the need for a Sammy pretty much a thing of the past.
C.2) The Stealth Issue:
Now, you need to get inside a facility, with narrow corridors and do a classic extraction scenario. You can't send with waves of drones, armies of spirits or hack-and-slash your way inside. You need a Samurai to support you once inside, if the going gets tough. I say wrong, with a caveat: I have to accept this is one of the scenarios where having one wouldn't hurt. However, the Combat Hacker, and you want him inside in many cases so he takes care of maglocks and maintains the team's node going, can stealth himself inside as well. Just get him the skill or the Skillsoft for it.
Now, suppose the extraction team is composed with one mage and one Combat hacker. Outside there's teh rest of the team: another hacker/technomancer and the rigger. Such a team can hit nodes stealthily and open doors, cancel alarms and have the building work for the pc's instead of against them. Mage has drones, spirits and watchers. They do scouting. And yes, mage has drones: He relies on Pilot agents and good matrix security measures, this relieves the team's rigger's commlink on less critical drones -sensor pods, easy to maneuver fly-spies, repeater drones, etc-. He also has tons of sensors on his person that feed him intel on surroundings. They can bypass almost any barrier: both can shoot, one can deal with astral badies and the other matrix threats.
C.3) Etiquette and Athletics.
This is the easy part as rarely the Samurai is also the face of the group. He needs so much in physical attributes that charisma is his -usually- dumpstat. Athletics are almost a moot point, since either it can be covered with magic (levitate instead of climb), and even if you have tons of it you'll need to help the team members that don't have it.
As an ending paragraph I'd like to say that a team of 'runners is best covered when you make slightly redundant, heavily supported characters. Don't be master of one, jack-of none. Generalists, when supported by another character who can do similar thing -maybe with abit less expertise than you-, can go over the specialised and in more situations (E.g: Mages with a bt of infiltration, athletics and computer. Also some driving skill could be nice, or easily covered with Pilot agents) . They can tackle variability and adapt easier, this kind of team build focuses on specially talented team members (technomancers, mages, adepts) and highly technological users (Hackers, Riggers). These guys, with the resources a sammy spends on his body, can easily overcome huge threats.
As a side note, software and computer skills would be a must for this runner team. As well as technical and programming skills: the team will eventually want tobe able to produce items, software and other goodies -desktop forges, programming suites, forgery for some extra cash, etc-. The sammy takes the place of a valuable team member and doesn't offer much.